Man, you just brought a tear to my eye.
You are in the same boat I am, with all those power hungry items in 1 room and all the extra breakers. I have three 15A breakers, and a 20A breaker in my office alone for that stuff.
Put the 12K BTU in the window & make the 5K your chiller. You can make your chiller cycle just as if it was on normally and just cool the water down just above the dew point and not have to worry about condensation. Granted you will have a 12K BTU running in the window, but the 5K will be cycling on only so often.
The larger the volume of water you cool the less it will cycle on, but the durations of cycles will be longer. Why have you been toying with the idea?? Execute it! Look on craigs list if you want to practice first on an old POS 5K btu. I would suggest a brand new one (if you have the funds) for a new chiller because the evaporator will be so much cleaner and not rusty.
What case is that you have? Looks pretty spacious. That fan displays the temps? That is pretty cool too. It would take me a while to design a new board waterblock and since there are already many other manufacturers out there it I can't compete with volume or price.