Downside here is you have to pay your 401k back and are limited to the lesser of 50k or half the market value of your 401k.In either of these scenarios, I think you need to evaluate the details as a whole with numbers. 

If I were you (and there are many things I don’t know about you) I might put half into cash flowing real estate at 60-70% leverage (to get depreciation, loan pay down, cashflow, and hopefully appreciation) and invest a large portion of the rest into something else.

In order to qualify for real estate professional status, you need to spend more than half of your work-related hours dealing in real estate directly, or more than 750 hours during the tax year.

Cut those numbers in half of you're single (or get married?). 

Half or more of that money will be eaten up in closings.  

Hello! I'm a new investor and just recently purchased my first deal, a duplex in a small town. The one side was move in ready and currently hosts a long term tenant that covers all the bills for the property. The 2nd ...

It's still white-hot, but not absolutely euphoric like the last year and a half.

If you purchase a property for $100,000 with say $20,000 down; and 3 years later sell said property for $140,000 while the mortgage has been paid down from $80k to $70k, that’s a cash out of $70k, or a $50k gain that can be used to pay down debt.Of course the easiest answer is to marry someone with no debt instead. 

Within our market the single family home has been evaluated at around 189k at 1554 living Sq with a 4 bed 2 baths and sits on half an acre.

Under the IRS rules, a person  qualifies as a real estate professional if: (1) more than one-half of the personal services the taxpayer performs in trades or businesses during the tax year are in real property trades or businesses in which the taxpayer materially participates, AND.....(2) hours spent providing personal services in real property trades or businesses in which the taxpayer materially participates total more than 750 during the tax year.Like @Greg Scott and @Russell Brazil mentioned above, I don't believe that you would qualify as a REPS, but if you are going to try it, make sure you document it very well (i.e. with some kind of proof, like time cards, mileage forms, and/or receipts, etc.) so that just in case you do get audited, you at least have something to provide to the IRS agent.