Re: questions for first build!
If it were me, I'd go for the Dyno without a second thought.
My wife has a GT / Dyno Kustom Kruiser (no motor), and it's a really nice bike. Nothing special, just a simple single speed Women's Glide cruiser. I have a Cranbrook that I motorized, and the difference in quality between the two is obvious.
I also think you are correct on the geometry of the Dyno. My wife's bike is definitely more comfortable for me than the Cranbrook is.
I went for the cheapest bike with my build, knowing that I'd either sell it quickly and build another, or end up changing out most of the parts on the bike. Not to mention, at the time, I could not find a good quality used cruiser. (I was looking for either a GT / Dyno or an Electra.) I should have been a little more patient, as I've since found a few of each on my local Craigslist.