Efrain,
Go to the ShopTalkForum.com, Type 4rum. Lots of good T4 info here. Several 912 owners who have done T4 conversions have posted their experiences. Do a search for 912, then search for your other questions. The things you must deal with include engine cooling and exhaust, which are discussed in the posts.
Good Luck,
Mike
Here is a car that may interest you:
http://members.home.net/jecole/912_24.htm