For quick summary, the Dell Latitude line that the E6410 is part of is a great series of business laptops. They are very serviceable due to a large number of replacement parts and their ease of use and repair. From what I know the E6410 is one of the last Latitude models to feature a full 7-row keyboard, which some people--myself included--consider a major selling point. That specific model is from around 2010 I believe, but the hardware should still be good enough for basic usage. The Latitude line is loved by the open-source community, so there is no reason why they wouldn't be compatible with what you want. While I have not personally owned a Latitude model (I have used one, it was either the E6410 or slightly older), they are often compared by enthusiasts to the ever-popular ThinkPads for the very same reasons. I will go over some of the other talking points below.
When businesses clear out their old laptops for a newer line, they will usually sell large batches of them used, so it's easy to find specific models at good prices in fair condition. These laptops--top of the line during their initial production run--now go for much less but still give comparable performance to middle-grade consumer laptops of the current era, and if you pay a bit more you can even get a really high-grade one for much cheaper than comparable products. Because these laptops are often sold to-specification or with multiple builds available, you can find specific ones that were sold with better hardware than their siblings, and you can also find ones that were upgraded afterwards with replacement parts. As long as you make sure the seller is reputable you should have no trouble getting a E6410 for $100-$200 with a decent multicore CPU. For more information on pricing and recommended buying habits you can check
this guide.
I have more personal experience with ThinkPads, and there are some good alternatives if you don't want a Dell or see some faults with that model. (I prefer the ThinkPad series because I feel the build quality is a bit better, but YMMV.) Consider the ThinkPad X220, T420, and T520; they all have full 7-row keyboards and comparable hardware and power, with the X220 being smaller and lighter, the T520 being larger and more powerful, and the T420 being in the middle. There are also alternative versions available, such as tablet models with rotatable touchscreens and digitizer pens (eg. X220T), or the T520W which was marketed as and is capable enough to be a desktop replacement. There is also a good
ThinkPad buyer's guide available as well, from the same guy as the one above.
As for compatibility, I know most of the earlier Dell laptops have great Linux support, so I don't see why they would have any issues running FreeBSD or other setups. They use typical hardware in most cases so should be compatible with existing drivers. The Latitude model I used worked fine and ran Xorg and other complex applications without any hesitation. Drives and WiFi were fast and responsive, as well as typing and mouse movement. The ThinkPads I mentioned also have good support; I have been using a X220T with FreeBSD for nearly a year now, and it's been a wonderful experience and everything except for the fingerprint scanner works. I don't think mine has a Bluetooth daughter card, but if it does then that doesn't work either because it's based on a nonstandard board configuration. Didn't look into it because I have no use for it. Generally regardless of the laptop, unless it's some weird proprietary thing (eg. X220 BDC) or a fingerprint scanner, it'd be safe to assume it works with BSD/Linux. Linux packages also exist for the BDC and I believe you can even get the fingerprint scanner working.
Unfortunately I can't speak on the Dell docking station, I wasn't aware that there was one for Latitude laptops. I know the ThinkPad Dock Series 3 does work fine with FreeBSD/Linux though; it's all passthru so it doesn't need any specific drivers or support, and one dock works on all the models I mentioned earlier and then some. I wouldn't be surprised if the Dell one was similar in function, since they are competing lines.
I should also mention usability and comfort. Note that the intended primary control scheme for these laptops is using the "nipple", a small joystick-like nub between the G-H-B keys on the keyboard called the TrackPoint. When it comes to usability this is a great tool and one would be remiss to not try it at least once. I was skeptic at first but I can't live without it now, and I'm considering getting a ThinkPad keyboard or similar to have it for my desktop setup. However, all of these laptops do have touchpads as well in case you dislike the idea of using a TrackPoint. As for the keyboards, the X220T I own is a joy to type on; the keyboard feels solid with a nice travel time and only a slight spongy feeling. Doesn't beat a mechanical keyboard, but it certainly beats all others I have used on laptops. Some complaints about the E6410 in comparison to the ThinkPad is the TrackPoint equivalent is crap and the keyboard isn't as comfortable, but if you're used to consumer laptops it will still feel better than those. I think the E6410 has a chiclet keyboard though, where the ThinkPads I mentioned are more like typical curved desktop keyboards.
Overall, it would be best to do some research into what all models you can choose from, their specifications, and what you want from them. The E6410, X220, T420, and T520 are great choices for someone that wants the equivalent of a portable desktop computer, because that's what it feels like to use one. All of these models also feature (at minimum) USB2, DisplayPort, VGA, SD card readers, Ethernet, ExpressCard, WiFi, Bluetooth, Mini-PCI, 3.5mm audio in/out, and hardware switches for wireless connections. Some models even shipped with 3G mini-PCI cards already built in. The bigger ThinkPads and the E6410 may also have other ports and parts varying with build, including but not limited to USB3, PC/Smart Card, DVD-CDRW drives, BluRay, HDMI, DVI, eSATA, NVIDIA Quatro GPUs, and more. If you get the docks you can get even more out of them. If you're willing to open the laptop up, installing and replacing parts for these are pretty easy, so you can upgrade whatever you happen to get if it isn't completely to your liking.
The models I am mentioning are often considered the "best of" when it comes to their combinations of features, comfort, and power, and there are some practical reasons to not buy newer models. They will often give you better performance but at a higher price and without the great versatility of the older ones with how many ports they have. They will also have poor backwards-compatibility with the dock models. Many enthusiasts will complain that the build quality of these laptops degrades the further into releases you get. Besides negligible performance losses to getting these older used laptops, another downside is the screens are often smaller than the huge 4K+ ones you see on more modern models; however, both the E6410 and ThinkPads I mentioned offer IPS screens that look just as good if not better than more modern consumer-grade screens. I can say with honesty that my X220T screen looks nearly as good as my expensive desktop IPS monitor. The battery life is also significantly better for some of the newer ones, but there are larger packs and mods available that can extend the older ones to match or even exceed the stock newer models. As stated in the other thread, there is also an issue with graphics support; the later Intel integrated graphics will not work with FreeBSD just yet, but I believe Linux has a bit better support in that department. Graphics do work on all of the models I mentioned for both BSD and Linux and switching between terminal and Xorg works. The newer models often come with integrated Optimus cards which have support through the nvidia driver IIRC. There have also been improvements to graphics support in general in FreeBSD 11 since those posts in the other thread were made that may open up your options a little. Sadly you probably won't find as many people testing BSDs on laptops as Linux, so getting concrete answers on what exact newer models work may be difficult.
For further reading, the
ThinkWiki is a great source on all things ThinkPad. If you want to hear some rants on ThinkPad design, you chould check out
Louis Rossmann's videos; he also compares ThinkPads to other laptop models, and due to the similarities of the models the E6410 has a lot of the same pros that he mentions, including build quality and durability, typing comfort, battery life, and etc. I don't know of any forum analogue for the Latitude line or other Dell laptops unfortunately, but /r/ThinkPad and /r/Dell seem to have a good few posts on the older models.
I tried to give a good history on business laptops in general, because only considering the E6410 when there are other models and brands would be limiting... I might have gone a little overboard in hindsight (I need to start a blog to rant like this). I also have more history with ThinkPads so I apologize if it looks like I was shilling, but the Latitude line is certainly a great alternative and worthy of just as much praise. Just get one that suits your needs, slap a SSD in it, and never use another laptop again.