I'm not sure about the energy usage. Wouldn't you just be hooking this up to a gas heater? If that is the case, then you probably wouldn't need to keep it hot all the time - just warm enough to keep it from freezing. I assume your builder is from Cleveland, so he should know how to build the thing to keep it from freezing.
If you are going to use a gas heater, and that is the only type of heater I'd use on a spa like this, just get a 150K gas heater and you should be able to heat the thing pretty quickly. You might even go to a 250K heater just to be sure since Cleveland gets so cold.
I can vouch for the quality of product from Viking. Viking does build very good quality products. There is a Viking Spas company as well. They are not related as far as I know.