Have seen some input on this, but still unclear on a lot.

Situation: If the empire has a Star destroyer in a system, and the rebels have say, some troops on the planet. The planet is loyal to the rebels.

?1. Do the rebels get resources from the planet?

?2. Can the rebels place units there when they come off the build track? ( if it was loyal to the empire, could the empire place units there from their build track?

?2.1 if they do place space units how is a combat resolved and when? (Leader appointment etc.)

?3. What were the empire players options when the ground was taken via a mission card and his space units where still there?

Thanks in advance.

The rules reference is very clear on this. The simple answer is the rebels can't deploy units there nor build off the planet when build triggers after advancing the timer. The same goes for the empire if they had ground troops and the rebels just had an x-wing tooling around. Considering any enemy units present essentially blockading the system.

What about the resources then? are they also "shut off" for the rebellion player if he has a loyalty and the troops on the ground?

The Star Destroyer stops you producing and deploying.

Consider it that the star destroyer intercepts shipments of weapons, materials and supplies.

He answered your question. (1) The Rebels can have 6 troopers on a loyal system and the Imperials can have 1 lone Tie Fighter in space in that system and they cannot build using that planet's resources icons. So during the refresh phase when you are allowed to build, that system cannot add units to the build queue.

(2) Also, since there is an opposing force there, you cannot deploy units there either.

(2.1) There is no combat because you cannot deploy to a system with enemy forces in it. You can only have combat during the Command Phase and sometimes during the Assignment phase when an Assignment Action card is played. IE - The Scouting Party one Soontir Fel can do.

(3) Not much you can do except pull ground units from another system to remove the Rebel forces. If the system was loyal to the Empire, then you can no longer build with that system or deploy to it.

This is real simple:

RR Page 3: "A player cannot use a system’s resource icons to build units if his opponent has a unit in the system."

RR Page 7: "A player cannot deploy units to a system that contains a sabotage marker or any of his opponent’s ships or ground units."