I like kmeaw as well. I came from 3.41 and updated to the official 3.55 then used the recovery menu (hold power) to flash to kmeaw. To try and answer your questions..
#1 you won't lose bluray playback unless you have a fat (256 nand)
your slim will be fine, but still backup EVERYTHING just in case and while you have access to it.
#2 if you FTP'd everything to your PC as a backup, if you needed it you'd just FTP it back
#3. Which CFW(s) allow creating and playing backups of games? Hermes 3.41CFW is a great choice if you're coming from a dongle... because all of your PSN game and hacked eboots you've already got set up just work. Otherwise kmeaw I know also allows ripping + playing.
4. Back up managers - I used to use gaia and recently got hooked into the multiman train of constant updates. Both are solid, multiman is turning into the XBMC jacknife app.
5. Of the CFWs that can load backups. Which ones are fairly easy to install? I can follow instructions pretty well in most cases, but I really want to avoid a brick (as I imagine everyone does).
Hermes was easier than kmeaw because it just installed via the normal menu instead of having to go into recovery mode. mPros and cons to all CFWs. You may want to wait for a 3.56 or 3.6 CFW for access to PSN again, you might want to try Hermes and ditch the calculator/dongle.. or just go for 3.55 kmeaw and enjoy running all the new games with the newest updates etc.