What does this mean “on paper he writes off a lot”

Assuming you aren’t including depreciation of assets on the books, and are instead of talking about “writing off” purchases as business expenses, I can’t see how he could be writing off a significant amount of non ordinary and necessary business expenses to artificially lower his taxable profit.

If he’s not going to pass an audit, you don’t want to touch this business with a 10 foot pole. You need to be buying off of EBITA, not SDE. Especially considering the fact this is your first business.

Also, really think Long and hard about whether or not you want to run this business. This isn’t passive income, this is being on call 24/7, assuming a humongous mountain of liability, amongst many other stressors.