Monday, I went to bed thinking I'd have to give up on openHAB until another day and would just have to either A) get the web GUI to work LAN-only (w/ a follow-on security addition to use away from home), or B) convert the project to an all-SMS interface solution (text "open" and "close" for the system to respond.)
I was covered up with a long day at work Tuesday, but the options kept working through my head. I took Wednesday off to devote to this project, but before I got started, something was nagging me about having given up on the openHAB/MQTT solution too quickly. So I decided to start the day off by entertaining 30-min to tweaking around openHAB and MQTT to get it out of my system... about 1-1.5 hrs later I had it up and working! This then led to a number of break throughs most of the morning, and by evening I had things pretty well ironed out "on the bench" and was ready for installation in the garage.
Anyway, the beta release is now installed and functioning. I'm calling it "beta," b/c while it is functioning and stable, I am finding moments when there's a delay in delivery due to all the wireless communication links and synchronizations that must occur, plus the software is not as refined as I'd like. All that, and I still have a few remaining Phase 2 & 3 components I'd like to integrate over time plus I've thought of a few more improvements to refactor into the design in the coming months.
Here's the high level architecture diagram.