Why use 25mm HDPE bulkheads?
Those are about as heavy as the 3.2mm Hardox. 15mm HDPE has a real weight advantage and will do the job as bulkhead too.

Weaponpower with the Saturns. I suggest to look at Ellis's Tormenta's.
He used a secundary gearing with a timing belt and the original torque limiter of a big batterydrill.

Batteries. Depending on budget, but Lead, NiCd or NiMH are rather outdated now.
Even if you're really strapped for budget, the older batteries will cost as much or more, and eat away the weight you have.

Reciever, just use a standard RX/TX set, ain't that expensive anymore, and would last you a few years.