What radio frequency should I use?
Available unlicensed frequency depends on the region you are in. In USA (Region 2) you can typically use 915 MHz for RTK communication. 2.4 GHz is available worldwide but it may have different maximum power limits in different areas.
For more details see Wikipedia here
Can Wi-Fi Interfere with 2.4 GHz GXM Radio?
If the Wi-Fi in use is in the 2.4 GHz range, i.e 802.11b, g, and n, interference could be possible. The GXM radio hops between 2.4003072 GHz and 2.4832512 GHz, which is in the same range used by 802.11b/g/n. Since Wi-Fi uses a single channel, the Wi-Fi is likely to be more affected than the radios, but that can depend on power output, antenna placement, and other variables. If only a few Wi-Fi channels are in use and can be identified, you could potentially use the Frequency Zones setting in the radio to uncheck those frequencies, and the radio will skip them. There could be some limitations to this: if you are covered by FCC regulations, the GXM radios must hop on at least 50 channels, which means you should have at least 10 Frequency Zones selected.