OP, this question makes me bonkers every year as a former tax preparer. I apologize upfront if I come off snotty; it isn't directed at you. It is because as a former tax professional, your question was an every day occurrence and made me nuts. Reimbursements are what they are. You spent money and you were reimbursed for what you spent. You did not make any money on this shop. It should not be reported on a 1099. Unless your spend is significantly higher than your reimbursements, do not report them. When your spend is big money, you may need to keep track of reimbursements.
Mileage is a different story. I told all of my clients to keep track of their miles no matter what. If I could use the mileage to help them, I did it. My clients would show up with shoe boxes of receipts so I could figure out their business mileage When I haven't made enough to justify my business mileage, I take the personal mileage for the deduction. I've had to purchase new equipment in the last few years. I take the immediate deduction for equipment and let my mileage flitter about until I see my bottom line.
One thing you do not want to do is show a loss. If the IRS comes back and says this is hobby income, you're a done deal. If the IRS decides you're a hobbyist, it's virtually impossible to turn it over to business income. Will you have to pay more in taxes? Yes. Do you want to pursue this as a valid income stream? if the answer is yes, bite the bullet and pay the government for a slight profit. A good tax professional will work with you and get you the best deal they can. They need repeat clients.
The best way to keep track is set up a spreadsheet. Don't worry, if you think you have too much information. As a former tax professional, I loved too much information if it helped me get my clients the best refund or the least amount they needed to pay on 4/15. Then again, I didn't charge my clients for the extra hours, your tax person might. My CPA loves my spreadsheet and workbook. She can find anything that she needs without having to call me. It did take her years to figure out my system.
Why do I have a CPA, now? The family business has become bizarre and we need her to make sure everyone is on the same page.
The advice you received was flat out wrong from what I read in your post. Find someone else. No you do not report reimbursements. It's not income. It's money you spent and someone repaid you.
MA
Live your life in such a way that when your feet hit the floor in the morning; the devil shudders...And yells OH #%*+! SHE'S AWAKE!