If you choose to do multiple large plywood tanks you should consider buying the acrylic or glass in larger sizes and then paying them to have it cut. it will be cheaper then buying the smaller exact sizes you need. for example their os an acrylic company by me that will sell 8ftx4ft sheet of 1/2 inch cast acrylic for 430$ this of course is to tall for a tank, however, 8ft x 2ft is a good depth. if you want to buy 2 8x2 it will run you 395$ per sheet. the 8ft x2ft can be cut for an additional 50$. I've noticed this from several different companies as well. it will also be cheaper to buy sealant in bulk, depending on product. the best I've done is 2 8x4x2 480g for 1000 dollars, sealed but without plumbing or stands.