Frank, that’s a tough situation. Sorry to hear about the flooding. My python valve flew off when I was filling my tank last week and I got water all over the house. Cleaning up water is frustrating to say the least.Hope you and the fish are okay. I personally like the idea of the timer or auto shut off valve. Maybe you can set a timer to see how long it takes to fill...ie(maybe it takes 60 mins ) then take away 10 mins(set for 50mins) so that way you can do whatever you want and be back in the room when it gets close to being full.
downsizing to just the 300 with the rare polys/favorite fish might be more meaningful, less maintenance, and would be only one tank to take care of. Even if you do take a break, I hope you decide to keep it because you put a lot of money and time into it. Then you can come back whenever you are ready. (maybe 75g as hospital tank ?)
At the end of the day you gotta listen to your goals and values to make the most effective choice for you. Maybe do a pros/cons list of all your options and do some problem solving. Regardless of what you choose, would love to still see you on the forum from time to time. You are a favorite and cherished member of the community!