Hello,
Sorry for the late response.
1 and 2: As stated in the manuals SkyElite works only with aircraft that uses standard SimConnect variables and functions, some aircraft, mostly airliners, do no use the standards.
3: It is explained in the manual how to enter ILS frequencies. You can enter them directly in the radio device or by selecting a destination airport in the map. But also the SimConnect standards applies to this, if the aircraft do not use standard functions for everything, will not work.
I suggest to use SkyElite with a small aircraft first to learn how to use it, reading the manuals please. The default TBM 930 is good for that.
Take in mind that plugins like Working Title instruments can interfere with SkyElite and make it not to work. They drastically changed the internal functionality of the SimConnect interface.
4. SkyElite should be installed and ran only in the PC where FS2020 is, the access SkyElite from any remote device or computer from a web browser, by entering the IP of the main computer. This is also explained in manuals.