As some of you know, I work for Centric Parts/Stoptech.
We sell parts, we don't service them. I'd like to start a business rebuilding our BBK calipers for customers, as well as machining brake rotors...properly for customers who's only other option is to buy new ones at $300/piece. I have all the equipment to do it. I have the boss's blessing, and would like to start out small. None of our distributors offer these services, so I can get referrals from them.
I'd like to also sell service parts.
I want to start this out of my garage, but can find an industrial address to use for the official business...for free.
I know I'll need a resellers permit and a business license from the city I'm registered in, but do I need anything else if O don't have any employees? If I only sell services, rather than resell parts, do I even need a resale number?...I might have a workaround for resale stuff.
I am probably going to give you more than you are looking for.

DO NOT do a sole proprietorship under your social security number...
Here is why. If at some point you decide to get out and do something else, you will literally have to file for Bankruptcy to release yourself from any future lawsuits and liabilities. Ask me how I know....
Consult a business attorney to find out what your liabilities are going to be, the answers will blow your mind.
Because you will be rebuilding stuff (technical shit here) you would actually be foolish to not have a resale license, you will have to file with the franchise board anyway...
While you are speaking with the attorney, have them write up a release of liability for an actual work order that gets signed. You would be amazed at what people try to get away with.
Get a phone number strictly for business purposes.
File a fictitious name statement and plaster your cars with this name, those vehicles just became tax write offs...
Find out what you need to do from the city to have a sign for your business, you will probably not be allowed to have one at your residence.
Have all parts and materials shipped to another address, not your home. This will eliminate your neighbors from being the wiser... Otherwise they could make like difficult for you, because they can.
I am sure I am forgetting a whole bunch, lemme finish my above top shelf Margarita and my Baja fish tacos and I will get back to you...
GT