Maybe I'm missing something, but all the combinators I lay down inside have no power so the whole thing doesn't work. Do I need to connect it to something?

Same thing happens to me. The circuit chip is powered but inside anything I place shows it has no power. AND both contant combinators show as simple combinators, they don't show any input, although I have something returning a value connected to the "in" end and also have a decider also connected as witness to make sure there is input to receive

power inside doesnt matter. only power outside.
Make sure it's fully covered by power.

There will be no energy inside this combinator, and the outputs on it will not be visible, they must first be brought out to the power lines.

It'd be nice to have power inside so you can test circuits while you're building it.
Possibly replicate signals between interior and exterior, i.e changes you make are "live" which is probably possible.
Would be hilarious to see a tiny character replica running around inside the combinator that mimics your position.

But on the outside the entire combinator needs to be covered in a power field or it wont work.

Yeah, it's a nice concept, but the execution is lacking too much for it to feel as something useful.. nice try though.