Well, you've probably given up on anyone answering these questions, but I just pulled it out to play and will give it a shot:
1. Can AT-STs and Speeders actually enter the Bunker Entrance hex? The rules say both
first "no" (they can't go into/through the hex) just to say a bit later: "all units are allowed to enter the hex".
AT-STs and speederbikes can enter the entrance hex, they just cannot enter the bunker complex without first converting to troopers.
2. When i am about to move an Imperial unit but that unit is at the same macro-hex as my potential target (let's say the highest priority Rebel unit) do i have to move it anyway (just to fulfill the rule that imperials alway have to move)?
I think the wording of "must move" is a bit awkward. If you follow the imperial movement rules, the imperial would move to a hex with cover if already in the same macrohex as the closest Rebel Unit. If the imperial unit already was in cover and in the same macrohex as the closest Rebel unit then they've already fufilled the movement conditions and shouldn't move...where else would they move?
3. Can i reinforce Ewoks/Rebel Troopers right into the Imperial Bunker Box when i have an appropriate leader there?
I would say no...the imperial bunker box is clearly not a macrohex, and reinforcements occur in the macrohexes.