I'm meeting a guy tomorrow afternoon that has 15-20 rentals in Lansing, MI and is looking to retire soon.

That's a span of time you can't even fathom at your age.2)  BUILD a SOLID FINANCIAL FOUNDATIONGet your credit score to >700 (there's a ton of info on how to build your credit anywhere on BP or Google)Obtain or continue earning W-2 income (this becomes important when you want to obtain a mortgage down the line)Pay down any bad (consumer) debt and don't pile on any additional bad debt.Start saving.

Or are they transferring larger sums from other retirement accounts to get going?

We are hoping the building will save up for its own repairs and updates as we move forward.We are going to retain the current tenants at least until next summer, then slowly start increasing rent until they leave.  

I had a license when buying off the mls and saved buy side commission and lot of time...single family.

Check out themoneyhabit.org to see how one young lady built $2M+ in net worth and retired at 28 in NYC. 

I do, however, advise waiting until you are able to find or create a great deal that you can afford before investing, and those type of deals don't just fall into your lap, you must work and actively seek them out ... the sooner and harder you start looking for them, saving for them, and educating yourself on how to spot and find them, then the sooner you will find them.

So let's say I was making money in my LLC for the next year or two, then decide to retire/stop, then I have to close the Solo 401K.

The Rub:Currently I do not have the down payment, next year or the following, absolutely.Possible fixes:1) See if a commercial lender will finance a down payment, while I pay the owner for the next ten years or until a can save enough for a proper downpayment, all the while paying the down payment too. 2) Find a rich uncle, who is not afraid of the numbers.3) Find partners.Legality: Is it legal to ask for a lender to fund the downpayment?

I am familiar with spreadsheets, and could have made my own, but I am happy that David saved me the trouble.