I'm sure you'll find lots of threads on the subject with a little searching. 

I would pay attention to the subject areas managed by professional competitors, what is their average rent and the curb appeal, storage plus anymore common facilities that they have and the benefits of then, in respect to financially.Who is this guy anyway? 

Is their any competition in the subject area and what are their advantages and their average rent and occupancy?

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.

This is all best case scenario and subject to change.

HOA is not in the control of the seller and you're always subject to that two weeks prior to closing or 1 day after you've closed. 

Subject to: Give the owner 5-10% down and take over their payments.

If it’s neither do a lease option or subject to or master lease.  

Otherwise you will be subject to income taxes and a 10% penalty.

I went through Vantage Credit Union and got a 5% interest HELOC, later subject to prime with all else similar but no fees. 10 yr draw but $300minimum repayment from the start.