I can relate to every one that expressed them self and thought, ain't going to be easy, very expensive overhaul and maybe If you have the resources to make it happen, I will say... "Go for it"!
I can see what you want to achieve. Instead of having a chlorine pool you want a piece of reef where you could snorkel or even use a little tank for Scuba diving. Some kind of "Beach ⛱", I think it been done before, That could be in this hobby the "Ultimate Reefer Dream Tank".
This is my personal opinion and how I would personally approach that kind build if I got the resources to do something like it...
First of all, I will state from the beginning, the budget for the project. It might cost you the same or even more to overhaul a swimming pool for your purpose. (Trust me I'm a retired "CPO" Certified Pool Operator).
Second, because I'm not a Monster Tank seasoned Reefer. I will look for really big systems caretakers for advice and insight. "Here are several Reefer's that could help". I will go to a public aquarium that has this incredible tanks, take a "behind the scenes tour". Right on the spot you will see, "what it takes to make it happen". I will chat with them and even try to befriends them. "They got more experience, than I definitely ever had!"
Third, but not the last on all the questions that you will be asking yourself along the road. I think is very important ... Did I will able to keep it up and running for my purposes for years to come and risk free from one of my point of view? (Master Bedroom).
All and on...
-That it can be possible to set a backyard saltwater aquarium pool? "Absolutely posible" 100%
-That is going to be easy? "Absolutely not" 90%
-That it will need tons of hours of planning? "Absolutely 100%"
-That... "If I got the resources and I'm willing to do it" with all the added costs? "Who knows, but I will sit and make an assessment of what I'm looking for? "Absolutely 100%"
And finally...
If you or anyone are going to set this goals. That's going to be the building treads to follow on "big dreams tank".