The first decision you have to make is what do you want. Are you looking for a complete restoration or a street/strip car from that era? This will determine your starting point, as an example if you are looking for a complete restoration you want everything original including matching serial numbers, these are very hard to find so the vehicle you find this on may be in fairly rough shape and will need more work. On the other hand if you just want an era muscle car then start with the best body, you can then install a newer EFI engine if you would like.
All muscle cars are easy to work on and each one has benefits and drawbacks. The 69 Stang is a great car with lots of available parts, learning about them is half the fun.
There are lots of books on every muscle car that categorizes the numbers made, options available, local clubs,