RE: When you can't heat your space, heat your body!

Looks like you are going into the right direction.

These machines that need to be warmed up, is it necessary to warm up the entire structure or can you create a smaller space to temperature control? Like one large room instead of the whole workshop?

Because you could insulate that smaller area faster and allow all the machines to run.

And then as much as you are trying to get the heat up, there are obviously a higher limit too, so include in the design a vent that can be opened up to eject some heat if it rises too much (or just open a door)