The redstone is actually easier than it seems.
Basically, every copper golem statue pose outputs a specific comparator signal. I make the signal travel just far enough to power a repeater, which then deactivates the redstone torch keeping the sticky pistons extended. And once all four golems are in the right pose, the door is fully opened.
The lever inside was a bit trickier though. I had a second redstone torch leading into each piston. Then I had a repeater leading into that torch, then another torch leading into that repeater, connected to a redstone line coming out of four individual repeaters that activated when the lever is flicked.
TL;DR, the torches are deactivated, but the lever makes a circuit of repeaters and torches reactivate them, closing the piston door.
