I have finally found a decent way to power everything, i'm gonna use the following charging circuit that can charge at 4,2v or 8,4v. EDIT : Apparently this board CAN'T charge 7,4v lipo batteries (2 cells) even though it says so on the backside of the PCB, false advertising but i can still use it in combination with a step up converter.

I'm gonna buy a Lithium Polymer battery with high capacity and connect it to the board.