So… change the configuration on the modem out of bridge mode, and change the config on the router into AP mode, and use the 2.5Gbps port on the modem for my PC.

Have I got that right?

I’ve resisted using the ISP’s modem as anything but a modem, since they’re usually locked down pieces of 💩… do you know if that’s the case with this modem?

Indeed I did say the cheapest way :)
Are there any reasonably priced routers with the specs you mention?

That’s more pricey than I was hoping for.
I may just need to give it time for this stuff to go down in price…