Fantastic.
I think what I'll do, to start, then, is pick up an Edgerouter X and a Ubiquity AP for the upstairs area, which should be able to broadcast downstairs "ok". I'll then keep my eyes open for another AP that can Mesh with the upstairs one, hopefully wirelessly for now. Eventually I'd want to run a cable to the second AP/mesh but it's Michigan winter, too cold for that work right now.
When I find specific hardware I'll try to post it here in case anyone is willing to look it over and double-check that it'll do what I need it to.
Thanks! :>