As far as Fords goes Mustangs offer the best bang for your buck on aftermarket parts availability. The early ones are a very simple design and very easy to work on.
The windsor style motors like a little 260, 289, 302 or 351 found in early Mustangs have the best parts availability and are pretty indestructible.
Go buy a coupe (what they called the notchback before the Fox hit the scene). They don't command near the price of a fastback so you can get a decent runner without going broke.
Start tinkering on small projects. Like someone else said just pick small things that don't take it off the road for more than a weekend. Do a brake job, swap out the plugs and wires. Ditch the points distributor for a duraspark and an MSD box. Just basic maintenance and reliability projects that will help you learn about the car and won't overwhelm you.
When you feel really brave try rejetting a carb based on Siegs instructions. If you can do that you can open a shop.