Let them pay the deposit with a credit card.

If you pay off a property or owe more than it’s worth, you can still owe or not owe capital gains tax.

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?

They pay their bills on time and make good tenants.

So I was paying under the market rent to live in the property, then moved out and rented my unit and it’s cash flow positive.

There are cheap PMs, but I think you end up paying for that in the end. 

The worst thing is to pay for a service where you don't get a benefit.If you have STR's and actively manage them, then there is a good chance that you can treat the propreties as active instead of passive which will allow you to offset the losses with other forms of income such as wages, interest, dividends, gains, etc.

if you're W2 and full-time, hourly or salary, you should be able to go off your pay stubs for qualifying.

The paid off student rental plus the 2nd student rental helps pays off the mortage for 2nd student rentals and living expenses for me and my wife. the duplex was  cash flowing approx  $300 month with the old tenants We manage everything ourselves with some help from our family. 

Also, the credits are "use them or lose them" - meaning, if you pay $12k a month for a 100,000 skips, then you have to use them all that month.