The plastic A pillar trim is probably just stuck on by some of the butyl that seals the windshield. Mine was.
As far as installing a headliner, I thought it was relatively easy, just slow and you need to be patient. I pulled it taught in the middle from windshield to rear window, then worked my way out to the doors. Waited a day then worked out as many wrinkles as possible, and those that were left, got rid of (mostly) with a hair dryer. Metal clips for holding the headliner at the edges helps too.