I assume that this unit will recover any damage sustained given the quanta in your bank?
Hmmm... You can say so. Probably OP?
I don't think it should recover its HP. I'd model it on Scarab, which does not recover its HP after taking damage.
Seems very UP to me. Even with 6 on the field, the extra 6 damage per 10 quanta would be better spent on a 10|6 Dragon.
Your original idea of ATK|HP for each 5 quanta sounds more reasonable, but I'd still make it 1|1 by default.
Btw, is ATK|HP change calculated before or after attacking? (Note: Scarabs gain HP before they take poison damage).