+1 Forget the new bike assembly for learning. First, its an expense path to learning. Secondly, assembling a bike with new parts and where everything works does not result in much learning.

Pick up a neglected bike at a garage sale, thrift store, or from a neighbor. Tear it down to the frame, and rebuild it. Old rigid frame MTBs make great projects!

If you don't have a pile of tools, head to a nearby co-op. They probably also can provide an older bike to build up at negligible cost, as well as technical guidance.