To address your fears, some of which are valid.
Usually, sooner or later someone creates a program enabling FreeBSD to access a different file system, but your statement is correct, I believe. (Though I'm not positive and am too lazy to google).
There is now a live version of FreeBSD, FuryBSD, do a search for it on the forums. I only tried it briefly and it seems as if it may server the purpose that is served by a live Linux image.
For number 3, I don't know. I've found that FreeBSD has had newer versions of apps sometimes, but my main Linux machine runs CentOS-7 which tends to use older versions of things. Depending what programs you are talking about the fact that it's an older version may not matter, but generally, I've found FreeBSD packages to be up to date, or close to it.
This is true that sometimes there are no BSD versions of Linux programs. Linux has a far larger user base and this is just a fact of life.
As for systemd, I don't know. I hope not. There are still a few Linux holdouts, such as Void Linux, and while systemd hasn't turned out to be a disaster, on various Linux forums you see what happens when person who has a single user laptop gets to work on a server OS.