Let me know if you have any questions..... Ive done three in-walls over the last five years. Not saying I know everything but might have a few helpful ideas.
If you use a 4x8 beam across the back it will give you all of the space under the stand to use for storage.
Also, on the right end, I would recommend sheathing it with plywood for shear strength so the whole tank isnt being supported by the one 8' 2x4 thats in the wall. You want that baby strong in case of a big earth quake.
yeah i planned on doing that with the plywood. the whole thing will have plywood i dont care for storage under the stand my sump is going to be off to the left. again this is not the final product just an update