I have a base station and send correction over cellular network. Correction at 1hz
I also bought a simpleRTK2B MR Radio Kit but not used yet!
With base 4-6 km away there can be several centimetre vertical variation over some time. I think it’s related to the weather, it seem worse when cloudy.
Radio 4 constellations at 1hz should work from what I read on this forum. I think you can increase bandwidth at cost of range if needed.
For earth moving you can look at this tread (grade-control).
So far I made 3 fields (13 ha) with opengrade3D all designed with Optisurface.
Are you planning to connect the GPS to some commercial machine control?