for doubling up on gels it depends. Normally we don't do that, but there have been times I've done that where we didn't have a certain gel color we wanted but I found that by mixing two that we had it came out rather close. I'm not sure how much it would effect it but you should look into how much that will darken your light. As another result if you use two of the same gel colors it should darken the light a bit and most likely make the color appear darker as well. I know for a dance of ours I used two dark purples instead of one becuase for w/e reason they were coming out very much as white light.
I'd say some of the best things you could do for a question like this is to simply take one of your lights, move it to where you can change the gel w/o any worriest, and just play around. Try mixing a blue and pink or a blue and red and see what kind of light you get and if you like it. Also experiment with your specific instruments and see what effect doubling up on gel has.
while were on color...im looking for CYM colors. im hoping to get 4or5 sheets of each. what number of rosco is good for this(could be lee or anything but i like rosco). im also going to try to get a small roll of primary blue and maybe a few sheets of a nice light but not too light purple. what are your suggestions?
If you check out the rosco website, they have a whole ton of pages online that let you preview the colors and all. If you go in there and just do find, and seach the word yellow, you can get all there colors for them. Some with the others.