Spend a bunch of time at the track. You'll find that almost everyone you meet will be happy to chat and provide their opinion. And ignore them all
Seriously, just listen and learn.
You'll find far too many cars available lately, especially with the economy, many are turnkey. Check out racingjunk.com. A turnkey choice is best. Maybe it won't be exactly what you'd want, but you'll never know that until you spend some time with a car and find out what you DO want. And it will get you running right away.
With all the options out there, you'd be silly to build one yourself right out of the box. Simply put, you don't know enough to get it right. And it might be dangerous. A used car will also come at something like a 50% discount. And can include the trailer and all the "what-not" that you can't think of today that you'll need.
In the long run, you'll want a suspended car, but to start, anything will work. Wheelbase is not a huge deal, anything over 225 should be fine. A weekend at the track is not expensive: entry, fuel, and such will be a hundred, maybe two at a big race. For us, the biggest cost is the diesel to get to the track (often a few hundred miles away), we can easily spend $300+ in a weekend on fuel to get there and back.
Having friends to "crew", especially if they have no experience, is more of a pain than an advantage. They'll trip all over things, get in the way, and mess with your process (e.g. your consistency). You maybe could use one helper (many race by themselves), and it's best if it's the same person every time.
Getting involved is not hard, doing it well is. And that's all about learning. That's why I'd spend this summer out at the track, find folks who will chat and soak it up.