This is the only question you asked so let me address that.
The difference in skill level between myself -- someone who can find the one hammer I have in the house after searching for a while -- and an actual carpenter -- who sleeps with his/her hammer under their pillow -- is tremendous. In terms of speed, in terms of lower levels of mistakes and in terms of the quality of the end result.
I bought the same book I suspect you have and managed to service my own regs a few times before it occurred to me that I'm never going to be as good at it as someone who has done 20,000 of them. I find all the arguments about a 3rd party not being as invested in your safety as you are, to be entirely unconvincing. Servicing a regulator is a skill and skills are perfected by repetition.
R..