Re: frames, rims, tires, etc.
As always, remember you're asking for advice, not facts.
There's nothing wrong with a good quality steel rim. A heavy duty Worksman steel wheel with 11g spokes is indestructible. Heavy, but who cares.
A well built aluminum rim is fine, but adding a sheve and the extra torque from a motor, you'll need a strong, quality rim, properly laced, and not the 49.99 complete wheel from amazon.
Frame is subjective. I don't like aluminum frames because of vibration, and a strong alloy frame usually has thicker tubes, added gussets, and bigger welds, which negate any weight savings, and is more prone to metal fatigue.
I'm not a trek dealer, so I'm biased the opposite way. I think they're plain and ugly, low end treks are junk, and I don't see any reason to spend the extra money for a hi end trek when you can get the same boring diamond frame from a million other bike makers for less.
Engine fitment is a factor, too.
Your questions are too vague to provide a "correct" answer.
Are you going for a stylish, custom build, or a daily, mostly problem free commuter?
Search thru the forums and you'll find many examples of what works (and what doesn't. )