Every so often I might need to re-glue the nylon down but really no problems here either. Don't forget you need to separate the kidney and butt plate unless you're going for ROTJ style.
Agreed, I've used snaps and they hold up great, even after close to 60 troops in my armor. I used snap plates (snaps placed into nylon webbing) and then gluing the nylon onto the armor. That way I don't have to drill into the armor and I can removed the snap plates if needed. I use E6000 to glue the snap plates down.
For the helmet, you can use the star foam, ACH military helmet padding, or hard hat liners.
For the armor, don't use velcro. It'll eventually wear out and fail. I only use it on my calves and have had to replace it a few times now. Go with snaps or the traditional strapping method.