Can anyone offer advice or feedback on their experience on how they utilize their Solo 401k to lend money to real estate investors? 

The industry is about people and personalities...and other intangibles.

A property manager will charge a fee to place new tenants there....you're also going to have to carry utilities while the home is vacant.If the tenants are happy, let them stay and enjoy the revenue while you stash that cash to be able to re-invest it into the property after they vacate. 

It is just as important as the rental home you purchased.This Industry has to do with legal issues, and many lawsuits, and if you don't have the best to protect your investment, then you won't be in this business very long.I know, it seems silly to think that by investing in a financial software program verse Excel will make any difference at all, but it truly does to the person you want to borrow money from.

Regarding HOA, I would introduce yourself to the management company and they typically have forms to fill out such as contact information and where to send the bills.Typically your closing agent on the closing statement has the first month paid for on HOA FeesAlso - confirm what utilities are included in the HOA costs

Yet in the Landlord Business (our Industry) people don’t view it as a business.

We didn't take the loss through the years for the original cost, just the operating cost like taxes and utilities. 

It may be accurate to say that I don't yet understand how to properly utilize the equity I've built in my properties, but I plan to learn.

From what I've read and through my brief interaction with a lender, the rentals need to be traditional and I need to provide a copy of the lease.I know Quicken Loans allows refinancing through Airbnb income alone but is the rest of the industry just too far behind?

They usually pay all utilities.