I have put crystals on 3 dresses. I found that it was a lot of fun and I was proud that I did it myself. The first one, I made a design on paper, then basted the design onto the dress with contrasting color thread. Then I glued the stones making sure I stayed away from the thread. I was worried about the same things you're worried about but it turned out ok! I like to do crafty things but I had never done something like this before.
For the second dress, I dreamed up a very simple pattern with a 34ss stone in the middle with four 20ss stones around and repeated that a few times along the neckline of the dress in a V and it turned out really pretty. Simple but elegant.
My third dress I just did this weekend. I didn't use a pattern this time - I just put the stones on randomly. I divided the stones into 2 piles, one for each half of the dress bodice, and just started out randomly gluing on each side, trying to keep it balanced, then adding in wherever I felt there was too much empty space. It turned out great!
On all 3 dresses, I outlined neckline with stones first. I also did the straps on the first dress. For that, I just eyeballed to see if I was gluing the stones on with approximately the same distance between each. I am pretty sure I used less than 100 stones on the first dress. Second dress was even less, and I used an entire gross (144 stones) on the third.
Good luck if you decide to try it!
I also used e6000, and I read the hints and tips on icemom (great blog that is not current but you can still access the articles). I also sew - if you can sew, I am sure you can do this! Don't forget that no one will be looking at your dress up close except yourself. Any minor imperfections will not be noticeable on the ice.