First of all, I want to say that I'm not an RF expert. I just picked up some stuff while working with this hardware, but I never actually designed anything myself.
1. Correct, if you don't care about sleep modes.
2. Correct. But I would bring out other DIG pins and SKY pins on test points on a prototype board, just in case.
3. It should not matter which pin to use, but I'm not sure about proper decoupling, you will have to figure it out yourself. I would try to find some examples of such use of balanced outputs. I would also at least put a series capacitor, you can always short it later.
4. Probably just ground.
5. Connect as described in the SKY documentation. For such high power you would need filtering and matching networks, otherwise you will have a hard time passing any regulation tests.
6. In the HAL there should be a setting names ENABLE_RT_TX_INDICATOR or something like this. You need to enable it and recompile the HAL.