If your printer is not listed, that means tplink does not test that model with the WPS510U, so cannot say it will or will not work.

I don't think that devices connected to the 4G router can get the SIM's phone number. Do you know how that happen? Does anyone know the admin password to access the router can get access to sim info?

Did you login the MR3220 to configure it? Remember to change the internet access to WAN only. The WAN connection type should be Dynamic IP based on your description. Check if there is WAN IP address....

WR849N? Is that a tplink model? If you have to reboot the router to get wireless connection, check if firmware update available.

what's the model number? hardware and firmware version?

no model number? how did you connect across the adaptors, via Ethernet or WiFi? If WiFi is slow, change wireless channel and channel width. If Ethernet is slow, or both, change cable, update firmware.