If the answer is yes, then it's a no brainer to make minimum payments on your 2.8% interest rate mortgage, and use the funds that you would have paid extra to pay it down faster, to either invest in more real estate, the market, or anywhere else where you can get a ROI > 2.8%.If the answer is no, then feel free to aggressively pay it down as fast as possible, to become debt-free faster, and just have a large amount of money in savings or to splurge with.The bottom line is that your 2.8% mortgage is GOOD debt.

Feel free to reach out.

However, with the rates and conditions of any triplexes and fourplexes we could find (we did find one, but it's in the Pendleton Heights suburb of KCMO, so we were worried about it being too dangerous of an area), we were wondering if it's worth it to buy a duplex and rent out the other half to help pay the mortgage, or if it's more worthwhile to rent an apartment and try to save up to buy a residential or commercial MFH later?

Start with BiggerPockets Ultimate Beginners Guide (free).

Don't worry about what it was listed for previously, as long as it works within your calculations. 

@Kyle Trotman feel free to reach out. 

.: I think you meant to type was… Thanks @Jeff S.for your free professional advice.

It includes HVAC filter and a few 'free' things (like one free lock out or something like that).

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I'm actually hosting a free cold calling challenge in January actually!