Hi Johnathan, Love Kansas City!
Well with a line of credit, it's like having a credit card with a predetermined available balance. Ready, aim, sign. You don't have to go through the "wait and see" approval portion of the process of purchasing with an individual loan (these loans qualify the borrower AND the property, a LOC just qualifies you and you qualify the property. Greater control, greater responsibility.
You can actually do both though, if you want. You can use the line of credit to increase your down payment or to buy down the primary lender's exposure to get a better rate. Read the loan/LOC docs but if it's descretionary then you might be able to use the funds for closing costs etc.
Your note says "rental" properites so I'm going to assume your a buy and hold not a buy and flip strategy. If you're a buy and flip guy, a LOC is great because you can essentially pay "borrowed cash" for a property and negotiate that way - keeps your closing costs way down to get in and out of a property. If you're a buy and hold (5+/- years) strategy then you won't feel the same level of hit on the getting in costs.
You can get the same qualifying guidelines for up to 4 dwelling units under roof and there are effeciencies in volume. I'm going to suggest you hunt for duplexes, tri's and quads.
Hope this helps.
Good luck, have fun and make money!