You'd need to figure out terms and have a good contract written to protect both parties. 

You should also consider protecting yourself legally by forming some sort of entity or business structure that will technically own the home.

Does anyone know the best way to accomplish this with a minimum tax hit, while of course maintaining the "no funds commingling" for asset protection?

Just be careful to protect your Personally Identifying Information.

Hello all.I’d like to know what’s the best way to structure my real estate business for anonymity, asset protection, and the best tax advantages?

LLC is meant to protect you the LL by separating your personal finances and liabilities from the rental property.

A real estate business would form an LLC (or other entity) for either tax purposes or asset protection.

Since it was a mechanics garage do you have an understanding of the environmental conditions that come with this type of asset?

For further enticement the return could look like this: a certain % on their money for what is called a preferred return (they receive this before any profit sharing) and then they receive a % of any profits that the property makes in any given situation, Fix & Flip or BRRR.There are many ways for this to work but you will have to understand exactly what your private investor is looking for in a return and you should provide them with assurance that their investment is protected as best as it can be via things like them having 1st position on the deed, promissory note signed by you for repayment, the property is purchased at such a discount that if you had to sell it in 30 days in its present condition, they would receive their investment back from the sales proceeds, etc... 

I think the duplexes would be better in terms of phasing the construction with the bank, and I know in my city anything over 4 units needs to meet all the efficiency and environmental guide lines, which drives the cost of materials.