Information got from USCIS teleconference:http://www.aila.org/infonet/uscis-teleconference-nepal-tps.
1.Filing i-765 on no.16 category both are accepted but to be specific c(19) is the correct one if its initial filing. and a(12) is for TPS already approved or its re-registration for example in other country cases that has already been granted TPS.
2. It's always good to send separate check or money order for both forms and fees. IF alrady a single check has been sent USCIS will still accept it.
3. Again good to send notarized copies of supporting document if possible, but only copies will also be accepted.
4. Any one here in USA on June 24 2015 can apply if they have all the supporting document as indicated on USCIS website. If someone wants to stay beyond TPS expiry, always maintain the lawful status you have now.
5. TPS is completely different application which won't be related to your previous visa status. But to come back to previous status after TPS ends the lawful visa status criteria has to be manintained before TPS ends.
Good Luck to everyone to apply despite of your status.