What do you suggest as some good options for me in this situation?

That's going to be your best option on such a short notice. 

However, I'd be curious how the second position lending would impact buyer's option for assumption.

Chelsea,You have a couple of options you can use a DSCR program to close in an LLC or a Portfolio loan program.

If you have an "early buyout termination" clause in the lease he is free to use this option. 

There are a ton of options for your primary residence to ensure you can pay down your mortgage (while living there) and make it a viable rental when you move into a future place.

I also welcome perspectives on utilizing a HELOC, other financing options, or keeping my primary mortgage-free.

I'm being told I have the option to buy it down to 5.75.  

I'm basically looking for something that glazes over or goes in depth about how an investor can set themselves up with as many options as possible to go about buying, but I can't seem to find anything.

There are other options like Citi and Navy federal that offer secured cards that graduate but some take a long time to graduate.