First off, I don't entirely disagree with Drak, but I would offer a piece of advice based on how I started. I bought a piece of MDF (medium density fiberboard). It's cheap as heck and easy to cut and carve up. I did the same thing you suggested, made a front and a back and carved out the pickup holes, neck pocket, and the control cavities on the back. It was a great experince for me to work with shapes and get comfy with the tools and stuff. You'll make a ton of mistakes. It's all part of the process. You'll also learn tht routing is a pain if you don't have templates!
Next I bought high grade oak ply at my local Home Depot. I did the same excercise but to a higher standard and planned to use these as my templates. The cool thing is that I could screw them together, slip a neck in and it almost felt like a real complete guitar. Heck, I even put on the trem and pickups. It kept me going and got me pumped to build a real deal one and now I had my templates. The cool thing was that my oak ply template set had all the lessons I learned on the MDF test run. Plus the oak holds up well when used more than once for templates.
So in essence, whatever gets you started is great, especially if it was cheap. but listen to these guys, they know what they're doing and they'll show you how to make the most of your finished product. Party on man.