That's daft, sorry but it is.

The Empire spans an entire Galaxy I doubt if all the Empire's troops would fit on Endor, they certainly wouldn't be able to hide long enough for them to spring a trap on the Rebels (by the way he doesn't mention his fleet only that he has sent an entire Legion of his best troops).

Who would keep the rest of the Galaxy in line while they are off on this mission?

A Legion is 1000 troops and command personnel and that is on top of the troops that the Rebels would expect to find at such an important site.

So the second wave of troops should be beefed up a lot but the Rebels should come with enough equipment to take out the troops they expect to find, especially on an all or nothing mission like this one.