I had totally forgotten about an immersion chiller..... That's a must add to the list. So I am totally sold on the 15 gallon size, probably a keggle when I can locate a keg. I think I will add all the plumbing to this unit: thermometer, sight glass, and ball valve. This way I can use it for multiple purposes now and in the future without having to make further mods.
So that setup, thermapen, and immersion chiller. That should set me up for full-volume boils at my current capacity and prepare me well for additional all-grain equipment in the spring, yes?