from what wiki says black top produces more power haha.
well if ur gonna get it al imported, get a wrecked ae86 with the whole running gear if you can.
is up to you, ke30 would be very nice but i think there would be a bit more time involved in the conversion.
umm ive heard a w55 box will fit the 4agze,
http://en.wikipedia.org/wiki/Toyota_A_engine that should solve most of your problems with questions 2,3,5.
and google will have the rest of the answers to your problems :)