Hi Dan - I haven't been following this forum closely, so maybe you've already addressed this issue, but it's hard to give a good answer without knowing where your garage is located. In other words, if the lowest outside temperature you'll have to deal with rarely approaches freezing, your needs will be a lot different than if you live in the northern part of the United States.
Whatever, I think I can safely guarantee that one of those little oil-filled heaters won't get a detached garage to 85 degrees in the winter hardly anywhere you may be. You're also going to need to heat the racks directly. And if you are using one of those open designs, liked the Visions you mentioned below, you're going to be losing a lot of heat to the surrounding room.
You might consider posting your questions on the Caging Forum, as well. They have some helpful and experienced posters there. Good luck!
-Joan