@bopuc:
A1. You could technically check the Id tags at the top of relevant scripts over SSH, but that's probably more trouble than it's worth, given...
A2. Yep, you can just apply the latest hotfix via Update Your Kindle (or bridge via MRPI, since you have a sane JB). Both options do the exact same thing, only the install method differs.
A3. I wouldn't recommend anything past 5.11 (or, hell, even past 5.9 or 5.10) unless you *really*, *really* want it. See the numerous warnings about that in the Open Sesame sticky.
In which case (assuming A2 took care of updating the bridge): update, reboot, reboot again, reinstall everything but hotfix. The "everything" bit should include KUAL Booklet-coplate and running MRPI via ;log mrpi since you won't have KUAL working yet
.
(And I do mean manual reboots, not the ones already inflicted upon you by the update process).
A4. A PW4, yes, anything else, nope.