Personally I think it will look like arse when all together using the Gater stuff except the Handbrake boot and gearstick boot.
Go the Nismo seat covers. They are really good. A+
A, B, C panels are plastic and the c pillars can be very brittle - be careful on removal.
All clips break easily
As for the doors they are compressed fibre type timber or as you put it fibreboard.
the heat from a heat gun will remove pretty much all the vacuum sealed material. Getting the glue off is a different matter. Mineral turps or similar and a lot of rubbing
I hope it turns out well for you