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
Its just easier to manage a small mess one than a large mess twice lol. I havent seen anything that would leave me to believe there is a way to put too much tic on a die. Are they really nonconductive though? If you put enough of it in the right places Im sure it would conduct.
Technically everything is conductive. Given a large enough voltage difference electricity will travel through any medium. But thermal compound is made to be very low conductivity. The real concern is thermal paste getting into things like your fan later and jamming stuff up, also making your PC look nice and not like a grey goopy mess.