Jason.Congrats on the purchase.I think you should ask them to sign a new lease and that you're looking for an increase in the rate.

Requirement to provide habitable housing only applies to conditions with the property that the landlord has control over.

I used 0% interest credit card promo to finance $20k utilities to the property and it still needs 10K to get it in mint completed condition.

Too vague of a description to offer any real value in estimated cost and the cost of construction is increasing significantly right now in our market.

What's the best way to tap that equity without drastically increasing my borrowing costs?

Also remind them that you also have their security deposit and, if the unit is returned in clean, in good condition, and by Sept. 30th...that you will promptly return their security deposit. 

(these are inherited problems- I would never let a property get to this condition).  

Rent must keep pace with equity growth (appreciation) otherwise the investor is increasing their risk. 

I also love YNAB for personal budgeting and use it religiously (knowing your income/expenses to the penny is key to profitable money management), so for the past few months I've increased my savings by pretending I'm carrying a note on a BRRRR and paying money into an account as if I'm in the middle of a 6 month rehab phase.I recommend that if you haven't laid out a business plan yet, grab a pen and paper and start mapping out your goals and how you'll get there. 

The type, age and condition of properties can influence the amount of reserves.