No problem, JR! We're here to help and I sure got a lot of help when I was researching what to build.
Your plan of putting off the upper till last is a good one I think. I did that too. Got my lower done then saved up for the upper which gave me more time to research. I'm doing that again now with the second lower I finished earlier this month. I'm pretty sure I'm going with a BCM 16" LW midlength upper but like the DD LW as well. One thing about the middy, if you put an A1 stock on it, it looks like a compact M16A4 - and of course you could change to a sliding stock if you change your mind. Nothing wrong with the 20" barrel but a 16" is a great compromise.