In the current version, only 5G antenna has a uFL connector so you can connect an antenna to it. 2.4G use PCB antenna and cannot use external antenna. Of course you can modify the hardware but this is not suggested.
We may have external antenna version but no schedule yet. So no promise.
Yes the PoE module works for AR750. The PoE can output peak 12W in specs. AR150 doesn’t consume more than 3W when working normally. But it peak power consumption will be around 7 to 8 Watt.