The CPE in building 1 should be configured as an AP, while the CPE in building 2 needs to be in client mode: The device(s) connected to the client need to be set to the subnet from your provider with...

Good question. Probably to reduce production costs for the CPE210 - the new HW version comes with a smaller PoE injector (0,6A instead of 1A).

I guess the problem is in your network setup. But to say for sure, much more information about your network topology and setup of the devices would be needed. The difference between Archer C50 and...

Do you experience such delays on wired devices connected to the same switch which feeds the EAP, too?

No. It needs 24V, so you would need two 12V batteries connected in series. But use a stabilizer to ensure a constant voltage.

I still don't get your problem. In recent switches you assign an IP to the switch's interface of a VLAN. So, if you use VLAN 6 you assign the first switch's IP to the first interface on the first...