I had thought about a 2 vessel system but I don't like the idea of draining first runnings to a bucket so I can use the BK as the HLT. I'd go with the 3-vessel. Direct fire=gas burners right? Just checking.
I also thought about a HERMS system that I can rig up with current equipment. This reduces the burners to two, keeps it to a single tier and I may also be able to do away with valve 7 (go through 6 all the time). And yes, direct fired means gas burner under the MLT.