I have found the value for a character to absorb all elements. And I am closing in on full status defence (against negative effects). So far I've got the value to guard against everything except Slow and Stop.
Keep in mind this is for a completely unaltered FF7.exe!
I will post more info when I have it. The trouble is getting a value that doesn't defend against a positive effect (like Haste and Regen). Manipulate isn't a concern as no enemy I know of uses it. Peerless will be obselete because of max stats codes.

EDIT:
Value for "Absorb All Elements": -1
(all elements will be absorbed into your HP)
Value for "Full Negative Status Defence": 111181567
(every negative effect will do nothing, every positive effect will still happen)
The latter can also be used on the Status Attack address to inflict all bad effects on every enemy. Also, Manipulate was left out since I believe nothing uses it on the characters.
This is for "version 1" of FF7 (completely unaltered, except maybe by the Chocobo Patch).

This took me about an hour to pin down. Starting from the exact value for the Ribbon accessory helped cut the time down.