1) IIRC nellis was removed in beta 3, will be added later
2) i don't know about this one but my 2 cents goes for it being busy
3) the heading the runway points to
ex: rwy 30 will point to heading 300
rwy 24 will point to heading 240
4) you can't, ground crew doesnt assist in startup, the request you are saying is for the ATC to clear you for startup