But just running all the basic formulas; the 1% rule, the 50% rule etc nothing comes anywhere close to adding up. 

Best to check the zoning to see what you would need to do.I would not immediately jump to adding AC. 

There are so many benefits to adding value to the users on BiggerPockets.

We look forward to adding you to the Spartan family in 2019!

What are some first steps to adding square-footage?

Think of ways to overcome seasonality & focus investment dollars to adding amenities that boost your listing in the off season, you only have 1 door so work to make year round income.Happy to share all I've learned about vacation rentals, STR management, guest vetting, providing a luxury guest experience, & stretching that investment dollar in the STR space.

Started to added systems to my business and hire out the work with this project.

One may consider that code in an area may require a permit for something as simple as changing out a toilet, yet a rehabber can't possibly turn a profit if they pulled a permit for every single little item needed.With regard to adding square footage, changing configurations, etc, I would always recommend it be done with full permits, but on other items, I would not make the same recommendation even though it may be code.

Sounds like you will have a lot of good info to ad to the forums with your rehab experience.

There you can access everything.https://www.biggerpockets.com/profile/photoBut here is a quick link to ad your pic, it has to be under 6MB.