Step 1: RECORD ITStep 2: Contact the developer to inform him that you own the parcel.

If they pay then no need to take next steps but if they don’t then at least you’ve started the (sometimes long) process and are ready to move on to the next step (eviction).

@henry Clark has posted on BP exact detailed steps to create a self storage facility.  

Mortgage recasting is a great option for homeowners who:Have received a windfall, such as a bonus, inheritance, or proceeds from selling another property.Want to lower their monthly payments without extending their loan term or going through the hassle of refinancing.Are satisfied with their current interest rate and loan terms.How to Get StartedIf you’re considering mortgage recasting, here are the steps to take:Contact Your Lender: Ask if they offer mortgage recasting and confirm your loan’s eligibility.Determine the Lump Sum Amount: Decide how much you can afford to put toward your principal.Calculate Potential Savings: Use an online mortgage calculator or consult with your lender to estimate your new monthly payment and total savings.Submit the Request: Once you’ve made the lump sum payment, your lender will process the recasting and provide a new payment schedule.Final ThoughtsMortgage recasting can be a powerful tool for homeowners looking to reduce their monthly payments and save on interest without the cost and complexity of refinancing.

What's the highest success percentage method to find a previous tenant's new address for this? 

Ideally, this would be just one step in a larger plan to grow into multiple rental units over time.

I want this to be acceptable long term if I keep this method of financing. 

From there, you can move on to the BRRRR method with single-family homes—buying undervalued properties, rehabbing them, renting them out, and refinancing to pull out your investment for the next deal.

You might consider other strategies, like taking a home equity loan or refinancing to fund repairs, but consulting with a tax professional or CPA would be the best next step for your specific situation. 

@Treza Edwards "I am reading the Rental Property Investing book and implementing the method that focuses on cash flow and that strategy states you need to have $300 cash flow per month, per property.