Back at the OP. Think abut this. Processors are cheap! I find that typically, is better to toss a handful of cheap ones communicating with each other, as opposed to try to get a big enough one to run everything. Also, by doing multiple small ones, this forces you to break the project in multiple simple problems. as opposed to one big confusing one.
Oh, and its easier to start off with a cheap processor that you won't feel bad about messing up, because there's another couple in the bag.
I've seen so may people stress themselves out trying to design in ignorance. Just grab cheap stuff you can get your hands on and see what you come up with. If you get anywhere, you will have learned so much that whatever plans you had at the start will now be completely out of date and pointless.
-jim ee