Just make sure you are saving towards those slow months during the peak months, buy a deal at the right price (don't overpay just because its a turnkey STR or you think it will make more money than projected), and look into ways to increase bookings during those slow months with some marketing and operation tweaks. 

It looks like you are doing an affordable build based on the cost but hard to say since you didnt provide info on the build itself such as square footage and finishes.

I have been doing the anakysis on several rental properties and saving the results.  

My budget is slightly constrained for this first property so looking to save on purchase price and hopefully add value through renovations.

Can you share some info about the property?

True re the prior poster, re this helping the seller save their credit, if you buy sub-to you will dramatically raise their FICO since the mortgage will show on-time payments.  

I have 880 credit score, decent savings, and no other debt except for 300K mortgage on my primary residence (worth $1.5 million).

After this conversation and having an agreed upon vision, save it as a "Version" of the vision on that particular date. 

Eliminate debt, establish a budget, and save.

So, start saving now while you are in High School.