Not sure on 4.76.
Not much though. Can installs few PSN games and that's about it. You aren't going to be running any unsigned code or home brew
Oh there is quite a bit that can be installed - you're right about no home brew but there are lots of titles that work.
if 4.76 is latest, then no you can't do this. not sure how far you can get anymore without the PSID, that was patched even on older firmwares I believe.
Anyway there is a great section at ps3hax.net on their forum that I used while I set mine up. It's not a fun process so beware!