Start with the trim pieces around the rear hatch glass. They are held in by clips, so just pull them inwards towards each other. The lower one is the same way, clips all around the edges. You can use a trim tool, or anything flat that you can wedge under it to pop the clips loose. Check by the rear window glass latch (with the glass open and lift gate closed) to see if there's a screw that's holding the lower trim piece in place there or not.
Since you're coming in through the headliner, you may want to keep your wires high, run them along the roof, and come down one of the A pillars into the dash area. For the upper B and D pillar trim pieces, they should be clipped in. The C pillar with the seat belt, are clipped in, and you'll need a T-50 torx bit to remove the seat belt harness bolt. Some A pillars are just clipped in, others have a single screw behind a plastic cap plus clips. Taking those out should let you lower one side of your headliner to pull the wiring all the way to the front.
I think that covers most points. I'm sure if I overlooked something, someone else will chime in and fill in the gaps.
