1) Get a good pair of carpet type scissors. You can use them for other purposes.
2) Whatever method you use to locate holes (ie. Measuring, sharp object from underneath where possible), consider using a hot single-pointed soldering gun to burn holes in carpet for seat hold down bolts and seat belts. It works beautifully and leaves a nice hole.
3) Also, if using carpet hold down strips, do not trim all the material away to perfection. Instead, get your carpet laid out, situate the carpet trim piece by leaving an inch or so of excess material outside trim area, screw down carpet, then cut the excess material with a good pair of sharp scissors.
4) anticipate all wiring before hand, add additional wiring for good measure, and measure and document where your wires are located, specifically.
5) Take your time
Good luck