I would advertise and re-rent the unit and retain that part of the security deposit not used to offset the lost rent.

Since acquiring a four-unit property on the Northwest side, my bi-monthly bill has typically been around $500.

You'll want a PMC that will check on the property monthly or even weekly, to keep the college students obeying the rules.This management may cost a bit more, but is well worth it!

We took loans under the individual name rather the LLC, would moving under LLC trigger a sale on paper?

Quote from @Brandon Blackmon: These prices will come when you get GCs (licensed, subs, and unlicensed) into the property and start to get quotes.

I put roughly 20% down on a $200k home, and am curious what steps I could take to possibly turn my original investment into a large portfolio within the next 10 years, when we're currently "low on liquid funds" after finishing up a wedding.... 

When it's sold it will be taxed as capital gains tax and may also have some unrecaptured depreciation which is capped at 25% and  recaptured depreciation as well which can be up to your ordinary income tax rate.

Looking to ramp up my business by advertising, specifically on Facebook to start.

Also, wondering if folks lend with the ability to only pay interest on the "drawn" funds during each payment to contractors?

Then the seller gets that exact amount for the property at times (it's a low percentage but it happens).