You should definitely determine between the two of you if this is ultimately a business or personal transaction because if he's insistent on getting his money back now that sounds to me like he is looking at it as a business transaction and if you are looking at it as a personal transaction that could be a considerable  obstacle for your relationship which may be the main thing to consider.

One consideration was to follow the WeWork or AirBnb model, create a website that handles the scheduling and payments, and create a corporation to run this through.

It isnt something Id give any consideration to due to the prevalence of them. 

Here's where you need an attorney to verify because the details of how you run it matter.Keep in mind there are financing considerations. 

Part of it is the limit of 10 conventional loans, but also debt to income ratio and personal credit considerations.   

(*) What metrics / facts did you take into consideration when evaluating providers?

Please see more below:Solo 401k vs Self-directed IRA:A Solo 401k has several advantages as compared to a Self-Directed IRA including the following which specifically apply to your situation:Unlike a Self-directed IRA, you can have the account for the Solo 401k at a bank or brokerage that does not charge maintenance fees and where you will have checkbook control.Unlike a Self-directed IRA, if you use leverage (which must be non-recourse financing in either case) to acquire real estate with your Solo 401k the income will not be subject to Unrelated Debt Finance Income taxGeneral Considerations Re Investing Retirement Funds in Real Estate:1.

You need to pay far below market value for the deal, bring an efficient rehab process to the project, and have your total all-in cost to be considerably less than what it's value is. 

New hi-rise condos have popped up, North Park has been declared an Opportunity Zone by the city, and even the VA recently bumped up their loan amounts in SD county, so now veterans are absorbing a portion of the market as well.It seems you have a 5-7 buy-hold plan.

Hi there, When my wife and I purchased our first home, we bought a condo. It is the first floor unit of 2 family home that was bought by a developer remodeled both units and converted the multi-family into 2 condos. A...