Install headliner
OH....i put the screws that hold the visors, mirror, garment hooks, and dome light back in. makes them easiest to find where to cut. I didn't have to make more than a 1/2" slit anywhere to get the screws accessible. You need to make sure your dome light wire is right where the dome light will be. otherwise, you may be fishing with a coat hanger for it.
I used the aluminized insulation like Summit sells. Just cut out pieces to fit between the roof supports and use spray adhesive to stick it. That stuff actually makes a big difference.