Thanks for the thoughts! I've started to use Laravel. It reminded me that, 5-6 years ago, I'd spent a while trying out an idea using CodeIgniter. My guess, from that experience, is that I could use PW or Laravel for this, but I'd have access to a wider range of stuff with Laravel. In the end, I wouldn't learn much about the real nuts and bolts of PHP or SQL, but if I get a basic prototype of my app running, I'll have a good overview of all the zillion things out there, how they can fit together, and how to put something together, at least, roughly, on my own. Which sounds like a good outcome, and useful if it goes further and I have to work with designers, developers, engineers. ?