Here+ RTK GPS - max range? other solutions?

I am looking in to solutions for precision landing on a automatic charging base station.

Is Here+ RTK GPS the way to go?

Is it possible to use multiple rovers on one base? what is the max range between rover and base?
The drone is connected to Mission Planner via RPI3 and a LTE Modem.

The Here+ is one of many options you have for this. Currently, it’s the lowest price setup I’ve come across that works.

RTK base to RTK rover (this is the unit that flies in your aircraft) is limited to 10km for any RTK solution and a given single reference station (base).

You can have one RTK base and many rovers.

An L1/L2 GPS may deliver the required position accuracy without a base, but your results may vary based on conditions unique to your system.

I use the S2525F8-GL-RTK with RTCM via NTRIP. (ESP32 + Wi-Fi/Lora/gsm) $130 including active GNSS/GLONASS antenna. No reason your baseline can’t be >10km . The introduced inaccuracy is roughly 1ppm (1mm/km). I have used base stations >30km away and easily have better than 5cm accuracy with an rtk fix. The rtcm broadcast from a base station can be utilised by any number of roving gps units.