I know of HELOC, delayed financing, and FHA (203)k loans but I'm not sure these will maximize my investing potential in the long run and I don't plan on living at the property.  

The entire process can run from $5k-$100k in severe situations (I've only witnessed one such repair cost that high).

This would all then possibly be run through an LLC to manage the short term rentals.

I had an O & E run and it shows a DOT and a mortgage of $56,000 borrowed 33 years ago.

This one is by no means a "home run" obviously, cause it'd be gone by now if so, but what i'm wondering is this: what if the right purchase price could make this an 8/10?

You may want to run some test ads.

However, you do run into issues of how you find the property to get under contract.  

A failed septic can run anywhere between $25,000 and $50,000.  

GET YOUR MONEY OUT WHENEVER YOU CAN and RUN AS FAST AS YOU CAN AWAY... 

I have a portfolio of 20 rental units and I used to use VRBO to rent out all of them, when I went to refinance with the bank I was able to only get very little out and when I asked the bank why they said it was because I was 100% vacation rentals on the entire portfolio, they suggested to keep it more around 70% long terms so I won't run into the problem again.