I say jump on the 81, parts are readily available. This is the moneymaker.
Negotiate the purchase of the large letter 72 first then the small letter 72, but only if she will use the shelves from the 96 to complete them. She can keep the 96 if she thinks it is worth a lot, although the compressor would be nice to have as a spare.
The slider has an Ideal coin mech. but is still nice......too nice to restore.
I wouldn't get too excited about that Cavalier 51 and the machine next to it may be a Westinghouse BV56 (leave it there) or a Vendo 39 (buy it cheap)
I can't help you with gas pumps although I think you may have enough work ahead of you with Coke machines already.
Nice find, especially all in one place
Keep us posted!