1. C52 is the 4AGE transmission.
2. C50 is the 4AFE transmission, C56 is the AE101/110 20V 5spd transmission. The C56 is geared for higher revving 4AGE's the C50 is not, but I hear the C50 will take a beating still.
3. most likely it will with minor modification, its still an A block transmission so it should go in no problems.
4. Did you miss my thread on transmissions last week??? I knew they should have made it a sticky!!!

here's the link so you can get some more info, read the whole thread.
http://www.toyotanation.com/forum/t75004.html
5. don't know.. never saw any reference to it on any of my searches.