Ram size.
All FP
Hannibalito I 32mm bore *80mm stroke
Hannibalito II 60mm bore *85mm stroke
Hannibalito III 50mm bore *75mm stroke

HP of LP.

1 of the main problems with CO2 is the fact all normal regulators don't like liquid. So, for the KISS principle, LP is a problem. The Trevor regulator (custom RW regulator, about the lightest , dependable regulator I know) doesn't suffer from liquid CO2, but doesn't regulate it either.

On the other hand, FP is a custom job, or a very expensive/heavy one. As 1000 psi pneumatics ain't off the shelf.

Buffertank size. I aim for 3times the volume of the ram. But in Hannibalito II and III I just used a customized 12oz paintball bottle. Hannibalito I uses a 2 oz steel buffer.

The 3 Hannibalito's also use a standard paintball bottle with an on/off valve, not the ones normaly seen in our events, the 20 oz bottles with a normal valve. We solve that by lugging our own filling hose, something you can buy at any serious paintball shop.
We have also a backup filling nipple, nothing more than a CO2 nut to a paintball bottle connector.

I hope that answers a few of your questions.