Wait until after paint to install the subframe connectors. You want your car sitting exactly how it will run. With no engine or trans, the front suspension will be extended.
Technically there might be nothing wrong with doing it that way, I know people who installed SFCs with the car on jack stands and the tires hanging in the air....but that is not the correct way to do it.
If I were you, I would paint the car, finish putting it back together, get it running and aligned, THEN put the SFCs on.