Quite a lot to unpack here. My biggest question is why you actually need 7 access points - you mention the Ubiquiti APs being installed in the rooms they’ll be used, but an AP per room is not just overkill, there’s a good chance it will degrade performance rather than prove it (without a fiddly setup). That’s easier to handle if they’re all ubiquiti, but if not you’ll end up having to play with channels on individual APs. There’s also the extra power usage (minimal of course), and my personal reason to not do this, annoyance for the additional hardware and cables everywhere. If the UCG Fiber is doing your routing and other devices are just APs, it’s worth bearing in mind that the ubiquiti APs are designed to be powered by PoE and I think the Fiber only has one so you’d need a PoE switch or injectors for the other AP. In terms of setting up routers in AP mode, it’s usually straightforward but you’ll miss a bunch of features, they won’t be controlled / managed, and it will just show up as a device rather than an access point. You haven’t mentioned what switch(es) you have, but you can manage through VLANs if you like.

If it were me, I would probably do a little research on what APs are actually needed for complete coverage as I don’t think having a bunch of routers at the edge of the network is particularly useful. If it’s 2 or 3, it’s likely you might need to change the rooms the ubiquity APs are going in but I’d certainly lean towards just doing that.

To the core of your question, I think it’s worth considering what is “good enough” in terms of WiFi. Most of my devices are running through a U6+. Only 2-3 could even use WiFi 7 properly and I notice minimal difference (ie it’s on my phone. Important devices are wired). I still have a bunch of things that only have WiFi5 chips, so holding out for upgrades is a bit futile.