3G dongles

I won't have broadband for a month, have to rely on 3G only. AIS & True have OK coverage where I live. Will have broadband again from mid-January so need a temporary solution.

I have an Asus RT-AC68U router. It does support 3G/4G dongles (but not necessarily all of them) so you can plug one into it and share the connection with everyone in the house. Oddly, the Asus website states that the only supported dongles in Thailand are the very old Huawei E169 and E176, while a great number of other dongles are supported in other countries. I don't understand why a dongle would work in one country but not in another (assuming they support the correct 3G frequency).

I have around a dozen internet-connected devices in the house (phones, tablets, laptops, a PS4) and I'd prefer to have them on the same network, hence would prefer to use a 3G dongle with my router & have everyone connect to it.

Two questions.

1. Can I get a 3G dongle (they seem to call them "aircards" here?) with a prepaid SIM from any AIS / True shop?

2. How likely am I to have trouble getting a True / AIS 3G dongle to work with my router? (If I can't get it to work, I might decide to use phone hotspot instead.)

(I also have a TP-link TL-MR3420 backup router in case it's less of a hassle as opposed to the Asus.)

Thanks