The Belkin RT3200 is a pretty popular router for openwrt. It’s a Wifi 6 router and you can usually find them cheap on ebay.

Most Odroid boards have arm processors, but the H3+ has an Intel N6005.

You can download Thunder from IzzyOnDroid (you can add this as a repository to F-Droid).

The communities on different instances are not the same. You can subscribe to both. The idea behind federation is that one company/server can’t control all the traffic. It might result in a little splintering of communities, but I think it’s ultimately better to be decentralized.

It’s easy enough to install LineageOS on OnePlus phones. Would rather do that than deal with shady stuff like this.

Faceit anticheat is very intrusive and requires disabling virtualization in bios. Also means no Linux support.