I’d like to use external modem/router (like ZTE mc889) plus an access point (like openWRT-able Netgear wax610, so I could use radius for authentication) with no additional router.

I just need 5G/LTE <—> Wifi. Would that work together?

If this device is actually a modem+router combo unit, then sure, you can do what you are suggesting. In that case, the WAX610 would probably just be a dumb AP.

If the ZTE device isn't a router with NAT masquerading (for IPv4), firewall, and DHCP, you will need a router... either between the two devices, or using the WAX610 as a router.

I'm not sure why you want to use RADIUS -- this is certainly doable, but rarely necessary except in large or complex networks (or obviously in business environments).

Thank you. I need Radius to keep track of who and when is online.

I’d like to use wax610 as a router. If it can run openwrtI suppose it can act as a router, right?

I'm not seeing this as a supported device.

Yup.... but now that I look and I see that it doesn't appear to be supported by OpenWrt, it makes this whole conversation moot, I think.

Actually not, I mean I will find another AP that is supported. Thank you for the general response.