Pick one radio and get a new battery for it. Pick two planes and get new batteries for them, and check or re-plumb the fuel systems. Also check your servo connectors for tarnish or rust.

Take it one or two at a time and you'll find your way. Everyone has their own style, so take your time so you can develop yours. You shouldn't need a new radio or really much new equipment at all other than batteries. And some new fuel I guess, it can go bad. I would say grab some new fuel but try the old stuff. If you have problems then try the new stuff and see if it makes a difference. Use the old stuff if you can but know it can cause issues if its bad.

RadicalRC.com is a good place to get quality batteries at good prices, and they have awesome links on their site regarding RC batteries.