david woodgate, I'd start with a tool kit like this. Get an inexpensive multimeter as well. For parts, I'd stick with dock connector, display assemblies and battery.
The industry standard for electronics and computer repair technicians and businesses. All the tools needed to repair iPhones, iPads, smartphones, tablets, Mac laptops, PCs, and video game consoles. — 50+ available at 64.95 each.
Go to the some of the more involved guides on the Step-by-step Guides under the phones icon to your right. Each guide will have a tools list like this:
Phillips #00 Screwdriver
Plastic Opening Tools
Small Flathead Screwdriver
iPhone 4 5-Point Pentalobe Screwdriver (if iPhone has external pentalobe screws)
iPhone SIM Card Eject Tool