No, you dont need to update incrementally. The best method of paste is personal preference, so long as there is paste and you remove all the things that say to remove them before installing. I use the x pattern usually just because Im used to it and I know it works. Youll know youve used too much when it squeezes out the sides, make sure to clean that off with a cotton swab. Good luck and congrats on your new build

1. Just flash the latest UEFI, and please do because stable EXPO speeds require the latest version.
2. At least the Noctua instruction booklet says 5 dots, if I remember right. It’s been running fine here (7950X which tends to get quite hot) with a Noctua heatsink.

Generally it's best to update if there's a major issue with your CPU that is fixed. It wasn't that long ago that the 7000-series CPUs had issues with motherboards being configured to over-volt one of the pins and melt the CPU from the inside (the updates have since rectified this).