Sory to rain on your paraid GreenRamper, but if you don't know how a bike goes together, and you don't have simple compatablility knowledge, then maybe a custom bike is not the way to go.
My friend got into biking about 2 months ago, and he realy liked it and he was learning realy fast, then he felt like he needed a custom bike. well, he got it together(with a LOT of help) and it was all good for a while, but then he didn't know how to do the maintenance on it, and his 1000+$ bike started to fall apart. He didn't know how to tighten loose spokes in his expensive wheelset, he didn't know how to maintain a euro BB, it was bad.

Well, moral of the story is, "don't get ahead of yourself".

Thanks for reading my compelling story, and I hoped it has swayed you.