^^^^ yup what Jake said if the gaps a really big then cut the qtr and move that. If you just need a little then I will add (at the most) 1/16 rod to the door but this is just to dial in the gap. As far as critical on the door gap yes it can be depending on what color you are going to paint the car. Some colors will make the gap look much bigger then it really is. One thing to keep in mind is if the fender gap is nice and tight and the door to qtr is bigger then it could end up looking bigger because they are not the same.
Also make sure that if you are doing the gaps that you have all the panels on, in place bolted tight. I've seen guys gap the doors to the qtrs and then put the fenders on only to find out that the door or qtr are now to tight and all the work they did to make that gap has to be undone!! Also put some weight in the doors to make up for the glass and window regulators and door panels. Those items have a lot more weight then you think. Just some food for thought