I know only about the status duration, which is in the ff7.exe file at offset 0x3B64F0 (at least in the German version, not sure about others).
It's 1 byte per status, 16 bytes total. The statuses are in the order: stop, paralyze, death sentence, slow numb, barrier, magic barrier, poison, sleep, regen, drain, shield, peerless (the last 4 bytes are unused). Just increase or decrease the byte you want to either increase or decrease the duration time of the respective status effect.
I don't know about your other questions, but I would assume that the damage calculation formulas are all somewhere in the .exe, too. (I'd be interested in this as well.)
EDIT: just found an old thread where nfitc1 posted the offset of the english version, which is at 0x3B60F0:
https://forums.qhimm.com/index.php?topic=13649.0