I love doing these kinds of projects. The core issue is you're trying to fit parts onto a bike frame that wasn't designed for them. The real trick isn't getting it to work, the trick is finding the right components, which is a trial and error process, without spending a fortune. I'd think a bike coop, assuming you don't have a big box of spare parts, would be a huge benefit.

I'm a little surprised that you don't seem to have a vision for the bike. I think that, since all of the parts on a bike work together, it's important to have a picture in your mind of the finished project before starting. What kind of brakes and handlebar controls are you planning to use?