OK. As you’ve mentioned Ardupilot you should ask those questions on their forum:
In regards to telemetry there are various options from a low cost set of telemetry radio with a range of around 100m to a WiFi system (range 40m) to a system using 3G/4G which is able to operate anywhere in the world where mobile phone reception is available.
Besides range, there is also the consideration of just using telemetry or perhaps later using live camera footage. In that case you need a system which can deal with such large amount of data. (WiFi & 4G can, some others can’t)
Also in regards to this you will get lots of info on the Arducopter forum.
In regards to ELRS see here: