Well, yeah, my ultimate goal was to try and use UT apps as my "daily driver" desktop environment. I never got far enough getting Lomiri running to see if that was possible, but hopefully it will get to that point eventually. I just assumed that to get the apps running I needed full UT running on the hardware.
I found that page on developing first, and that page has a lot of details but I was hoping for an (updated) overview. For example, the page that explains the Web App explains the webapp-container command, but nothing on where to run it or how to submit an app to the store. Various other documents mention clickable, the Ubuntu SDK, and some places mentions that some tools work on different Ubuntu versions and some aren't supported. I'm still not sure where clickable fits in. It all kind of assumes you know what all the tools are for, their history, how they fit together, and that you just need basically the man page of a tool instead of telling you what tool you need use in the first place. I did come across the UT programming course, but it mentions a lot of things that I think are out of date, so I'm not sure it is the best source. But I'm making progress and hope to be productive soon. My current best guess is it looks like you need to be running UBuntu 16.04 and use the Ubuntu SDK.
I found this video tutorial helpful by CiberSheep https://forums.ubports.com/topic/3347/videotutorial-first-steps-with-clickable