seeing this fills me with fear and awe. If you don't mind answering a few question.
How are you ever going to get anything from the middle of the tank?
At 48" wide and only 21" deep since it is a peninsula the bottom centre will be easier to reach than the bottom back of a standard 180gal against a wall. Also since The sump and all equipment will be in the basement I have made the stand 27.5 inches from the flooring to the base of the tank so the tank centre is at eye level when sitting on our sofa and chairs, making it easier to reach into without a stool. Still comfortable with a bit of a bend to look in while standing and allowing real reefers to view from the top down while up close. It is a bit below eye level from our pub height dining table but compromises are inevitable.
Have you planned for humidity in the room and are you going to use a fan and vent?
This tank is replacing my old 180 which did cause some humidity issues in the room until we added a room dehumidifier and improved some attic ventilation. I think that the humidity from the increased tank size will be offset in the upper room by the removal of the sump and skimmer and the change from Halides to hybrid T5/LED lighting. In the basement I will be taking down my 200gal fish and softies system and will be removing the pink insulation and spray foaming the concrete walls in the basement which I am told will make a huge difference in basement humidity and can make further changes there if required. At an overall household level I will also be taking down my last FW tank (a 90gal in the bedroom).
what is the potential weight with water, sand, rocks?
Should be just shy of 3000 pounds. The stand set the tank out a few inches from the wall to allow for painting the wall in future and to catch another joist running perpendicular to the tank. Also a key factor in the placement of the tank which makes our dining area a bit smaller than perfect is the fact that the main load bearing wall in the basement (no beam) runs directly (66/33) under the tank and at that point is supporting only the joists and not the ceiling or roof so most of the tank loading is onto relatively unstressed vertical members.
The thought of that cat falling in once its setup and drowning is giving me anxiety
Another one of our cats (the bad one LOL) once jumped off the top of a bookshelf onto the top of the bedroom 90gal in the middle of the night. Shattered the glass top, swam across...climbed out at the side nearest the bed and scooted (soaking wet) under the covers as we were waking up having heart attacks!!!
Once the sand and rockwork are in the tank all of our cats will easily be able to climb out on the rocks and in a bit of time when my huge magnificent colonies are breaking the surface with their many growth tips, the only consequence of a feline incursion will be the prompting of a big frag sale!!! LOL