It sounds like a lot of unnecessary work.
What type of wall surface? it can be very difficult to be accurate drilling a lot of holes for mounting letters. Have you thought about just using silicone or other type of adhesive? I've installed hundreds of signs and letters this way with no problems. Quick and easy. If the letters need to be standing off the wall, there are plastic mounts available that can be glued to the back of the letters. I haven't used them in years, and I don't know if they are available in your country, but a bit of web searching should find them. An added expense, but easier than cutting the letters twice, drilling holes, inserting screws, then laminating them all together! Also, 3M makes an excellent 2 sided sign mounting tape that's available at most local hardware stores here.