Just follow the guide, it seems very comprehensive.
A couple of extra points though, take a trip to you local car trimmer/upholstery shop, you may be surprised how close they can match to the OE material, personally I wouldn't re use the old lining for reasons already mentioned
The base panel that the headlining fixes to, has a tendency to go brittle around the edges, especially at the front end around the interior light, save any broken bits, and use them to repair the base once removed, repairs should be made with fiberglass resin and coarse matting... any decent DIY shop should have this...
Thom