Monroville said:

Cargo ships could have been kamikazis (or still loaded with weapons) - besides, the rebels can't be picky when it comes to ships.

Speaking of which, the rebels need a LOT more ships in order to survive:

(1) potential Executor volley
(2) massive amounts of TIEs and SDs pummelling them
(3) DS2 raking super laser through multiple ships.

I would almost decrease the number of Imperial SDs (being that if this is still a trap, you can't exactly hide a few hundred mile long space ships)

Depends on how big the death star or endor is plus it depends on if the SD's were already there
or not they could have just come out of hyperspace

I think someone else suggested showing 2 more rebel fleets jumping in from hyperspace as if to rendevous with the first fleet (where our heroes are) to show that the rebels are coming from different parts of the galaxy to converge at one point. I know they mention meeting at Sullust, but again, ...can't keep a secret hundreds....of space ships just floating around.

of course but thats it the empire doesnt really care as evidenced by: Vader: what about the news of the rebels gathering near sullust? Emporer: it is of no concern.