Adding an access point to GL-MV1000?

It probably won’t (be enough). You’ll have one band at a time (2.4 or 5 GHz) and it will be very slow, about half of what a decent AP can do.

I tried this before:

https://forum.gl-inet.com/t/brume-brume-w-gl-mv1000-configurations-ubuntu-openwrt/14004/2