Everything Buckner said is very good advice.

You're right at the point of wasting money. Don't do it. You'll only spend the money once instead of twice, and you'll start out safer. Don't waste the money on a power panel and heavy lead battery.

Go the safe way from the start. Spend the money on a portable power pack for your starter. Starters on long wires are a hazard. Spend your money on a portable glowplug igniter. Glow igniters at the end of a wire connected to the flight box are a hazard.

Combine the usual two wires from one flight box, and one of them is going to have to pass around the propeller. Get rid of the wires and you've improved your starting safety a bunch.

And the weight of the battery is something you're going to have to lug around the rest of it's life. For what? So you can have to deal with two wires and the prop the rest of your life. And you wind up with almost no flexibility thanks to those wires. With the freedom of the portable starter and igniter, you can restart with the flight box comfortably out of the way. The more experienced flyers restart stalled airplanes anywhere. Saves lugging dead airplanes back to the pits.

Safety
Convenience
Safety
Less dead weight to lug around
Safety

BTW, I'm editing in a picture of my flight box showing the fueling setup I use. Hand crank pump. The fuel jug is a thick plastic one I found at a kitchen store. There are only two lines in/out of it. One is the pickup and goes to the pump. The fueling line from the pump plugs into the vent when not in use. In use, I unplug it and the jug is vented. The hose nozzle is from one of the fueling sets for models. The piece you're supposed to stick on the model's cowl is the vent in the jug. None of my airplanes have that expensive stuff on them. It's on the jug and fueling hose. The airplanes are fueled through the hoses from the airplanes tank. Just disconnect a hose, fuel through it, connect it back. No cost. No extra building effort.