You need to pay attention on where the lights or fan placement, have seen alot of customers complaining about the placement and it is very very difficult for them to re-do it or shall i say cannot re-do it once the damage is done.

as for the cracks, the contractor is half right. you will see no lines after them fill it up and paint it. but you'll notice it again after sometime, probably 1 or 2 years later.