Some quick comments. Bradford White are highly regarded water heaters, but are supposed to be sold only to plumbers. This may or may not always be true and perhaps you are going to have a plumber do the job anyway. Point #1 I concede that fact that I am not a professional and that there are many things I am still learning. However, the cold water supply for all water heaters starts at the bottom of the tank. This is done with a dip tube which is a tube placed in the intake at the top of the tank and goes to the bottom. Therefore, having the intake at the bottom of the tank is really of no benefit that I can see. Here's how I plumbed my recirculating system. The return line is teed into the intake at the top of the tank. Works great and has been for 4 years. Point #2 Power vents are very efficient. They do not use a standing pilot light and are vented with PVC pipe. While they are more expensive, I recently priced a GE/Rheem and it was less than twice the price of a conventional vent heater. More expensive, but not 3X Point #3 You certainly have a lot of tubs! Do you really think you will want to fill them all at the same time? A big Jacuzzi might require a heater with some more capacity than conventional bathtubs, so you might want to figure that in. Point #4 I have no experience with radiant heat so I can't comment one way or the other.