[Christy,
I'm building a 360g plywood tank now. We are doing a tank tour on Saturday, and I'm the last stop. Join that, and I can show you everything I've done so far, and my future plans. Just really quicly, it doesn't make sense $ wise to build a smaller tank. (<100g) You really want to go plywood when you have a specific space to fill. However, a majority of the inwall big tanks are plywood. The glass thickness depends mostly on the height. Search for plywood tank on Reefcentral or reefs.org and you can find this chart. My tank is 7'LX32"Wx34"T, and I'm planning on using 3/8" glass. (Possibl7y 1/2 inch)
Sam]