Thanks for that clarification. several times is an understatement LOL..I've been enter a . (dot) for more than a minute and it's still not getting anywhere.Do what it says: type a . and Enter to give it more time to recognize USB devices. Maybe do that several times.
set kern.cam.boot_delay=10000
set kern.cam.scsi_delay=10000
boot
Okay, I have something else. It would be helpful if you could try this:
Boot the installer and choose Escape to loader prompt from the first menu (could be 2 or 3).
Enter:
set kern.cam.boot_delay=10000
set kern.cam.scsi_delay=10000
boot
Then see if it boots without any additional messing around.