Really get some 16awg , 18awg , 20awg. As for battery 12awg would be more than enough, but keep in mind more power will need a bigger awg. most of what you will want to use is 20 or 18 gauge. Also i use extra servo wire alot. 5v doesn't need much wire to be fine 20awg should do just dandy.
Also alway get silicone insulation as it doesn't degrade as fast and just is so much easier to work with.