You will then have a few options with that rent money....you can put it into principal or you can start saving it to purchase yet another property.

What would you do and what is the best option here? 

There are multiple options for the property, the hardest part may be deciding which one to pursue.

Before buying, do an analysis of the market that lets you in on its dynamics, link the type of property that matches your set goals and is in line with the risk you can take, survey the possible financial options open for borrowing money, and finally analyze the cash flow of this business before engaging professionals in managing this apartment complex.Conduct thorough checks on possible properties, covering in-person checks, money checks, checking leases, comparing market prices, checking rents, assessing the condition of the property, and looking over legal contracts.

Take a look at the find a lender tab or work with a broker who can quote you multiple options from a wide variety of lenders! 

The more I think about it, the more I realize that a Solo 401k is probably not an option for me because I will not have self-employment income. 

Before diving too deep into property searches, it's wise to first determine your financing options.

Most lenders will offer two options:1: 20% down and 20 yr amortization and 10 yr term.2. 25% down and 25 yr amortization and 10 year term.Rates will vary by region, lender, and relationship with your lender.  

Am I missing out on other options? 

You will then have a few options with that rent money....you can put it into principal or you can start saving it to purchase yet another property.