Doing a water test is a good idea. Once you drain it add the rock and sand and mixed waterProtein skimmers are pretty much a must if you plan to keep fish for sure and always helpful to coral also. It is best to try and vision what your wanting to accomplish and then set your budget and then shop and read as much as you can about the ones you like. Then make your choice! Many people sell on the forums which can save you a ton f you know what ya want.

Acrylic and PVC can be cut several ways . You can use a table saw,jig saw,circular saw,band saw.glass cutters,utility blade and they also sell cutters made just for the task at hand. God luck!