#1 on my list would be damage control and maintenance. Check to make sure your brakes aren't hanging up, run some fuel injector/carb cleaner through it, check spark plugs and distributor cap condition. Basically, check all the easy/common things. I'd also address the rust issue as soon as you can, its not going to get any better on its own.
After you know your car is solid, then I'd start with the mods. Probably throw a grill block on it first and get a mpguino!