When frigging with carpet, kick panel, seat, and door sill plate installations use an awl to locate blind screw holes; it will make life sooooo much easier.
When installing carpet, work from center of car to outer edges. Pre mark with chalk the center of all carpet pieces, and corresponding floor boards. Use spray contact cement to attach carpet to drive shaft hump, toe kick area, and 4 inches of floor inboard of door sills. Carpet areas not glued will flatten out with time.
Any trimming should be done a little at a time, nibbles if you will. It is hard to add carpet back to a cut once it is sliced off. Use a fresh utility knife with a good supply of blades, they will dull quickly, and once dull will cause trouble trying to trim accurately.
Cut a small ¼” “X” with the grain where seat belt and seat bolts pass through carpet once location is found using the awl, and marked with chalk. Chalk marks for seat bolt holes will make dropping the heavy buckets in place much easier.