Creative 5G+WiFi Wan Network Buildout with Separate Devices

First post, getting into networking. I'm a software, but not a network, engineer, been trying to reason through a network build for 6+ months, going crazy, so please pardon any ignorance.

I'm a fulltime RV'er, upgrading from a simple Netgear hotspot to a system that:

  • Manages an exterior mounted 5G modem/antennas for primary WAN
  • Manages an exterior mounted WiFi 6 AP in client mode only for WiFi as secondary WAN (campgrounds/stealing friends wifi)
  • Runs on an interior latest gen router with either WiFi 6 built in or using a second AP for interior device connection
  • Manages all of this through a single OpenWRT (or GoldenOrb etc.) UI such as LuCi, to eventually monitor via my extensive HomeAssistant instance

I'd rather keep my router separate from the exterior modem and AP so it isn't subject to Colorado temperature swings (-10f to 120f). I also want to be able to upgrade each of these devices separately on failure or improved technology.

I understand ModemManager etc. is closer to plug and play with GoldenOrb, I'm open to that route, but I cant find documentation that a separate "dumb AP" can be managed as secondary WAN with any software.

I have a UniFi switch and AP inside, and can't tell if flashing OpenWRT onto those would allow the router to manage them all in a unified UI, especially with the intended addition of an exterior AP for joining other networks.

Off the shelf products for my exterior setup seem to be combined 5G modem & wifi router combos, and I'm unsure if I can set the modem side of that as IP passthrough, and the wifi side of that as AP only in client mode, and manage them both through my interior OpenWRT router.

Open to just about any hardware (Ubiquiti UniFi or UISP, GL.iNet, BPi-r3 etc.) that can accomplish all of what I'm shooting for. The end goal is ideally having it in one unified interface, kind of like what UniFi does with its Network Controller.

Any help would be super appreciated!