For the documents that required for TPS depends.
You need to send the document to support and show that you are Nepali Citizen, and you have been living in US since June 24th, 2015.

can i go to school and be in f1 > You have to look for an option to go back to F1 status from H1, Change of status, Or you can just get an I-20 from college and do that route. Someone might have better idea on this.

is it possible to get Gc through TPS EAD > Yes it is, because you are in status right now. Find a company who will sponsor your GC.

IF I HAVE TO GO TO NEPAL,WILL I NEVER BE ALLOWED CO COME BACK > It is not 100% guarantee to reentry to US, but most of the time they don't stop TPS AP to get in.

MY VISA WILL EXPIRE IN 2016 MARCH > If you are leaving US on TPS, you must have AP, and TPS AP does not have anything to do with VISA expiry date.

IM IN H1B NOW AND GOING TO QUIT SOON > I don't know why you are going to quit (Hb1 is a good deal, I guess), but it's up to you.

YOUR ANSWER WILL BE BIG HELP > Hope it helps.