Hi Matt,
If it were me I would go with something a little stronger then 1/4" balsa for your servo support. You would be surprised at how much pressure can be applied to one of your control surfaces and in turn transfer that pressure to your servo's. I'd go with say 3/8" balsa or go ahead and use your 1/4" but glue some lite ply on top of it before mounting the servos.
With regards to your question about mounting your aileron servo you might do a search for the model that you have and see if a manual is available online. Some of the kit manufactures do offer that kind of support. Another idea is to go with a manual from another manufacture that may be similar to your and see what they did. I found this page that has several manuals online that might be helpful:
http://www.greatplanes.com/parts/index.html
Do a search on this site for idea's that might be helpful. I'd start in the kit builders section.
Post what type/name of airplane that you have and this will help others who read your post to better help.
Hope this is helpful to you...
Cheers,