What are the best methods to independently verify zoning and land use data to ensure compliance with local regulations?

For this I’ve taken the payment amount of the second loan and included it as an additional monthly expense.

Here's an article with additional FAQs on cost segregation studies that you may find helpful.

Additionally, the rental arbitrage strategy is not investing, its operating a business.... an extremely risky business.

Sorry one additional item I hit post too soon...The reason I asked about TIA is because you generally want to get a contractors opinion of cost prior to lease during that negotiating phase so you know how much that TIA covers and what you'll be coming out of pocket for.  

Also, what’s the best way to ensure the area is safe and desirable for tenants?

They charge $1250 for properties under $1mm for a 1 to 1 exchange and if you have another property to move your funds into, they charge $550/additional property.

Lenders may count eligible assets as additional qualifying income by dividing eligible assets by 60.🔹 Example in Action:Rental income: $9,000PITI: $9,500 → DSCR <1 (not qualifying)Using $63,000 in assets → Adds $1,045 in incomeNew DSCR >1 → Higher LTV (80% instead of 75%)🔹 Why This Matters:✅ Helps investors qualify for better financing✅ Increases borrowing power and flexibility✅ Allows you to scale your portfolio fasterUnderstanding financing tools like this can be a game-changer for investors looking to maximize opportunities.

I've got about $525K in equity in the property, but lenders have told me that I cannot get a HELOC to access that equity for additional purchases because the duplex was financed as an investment - they have said TX law dictates that HELOC can only be used on primary residences.

It is much better to have a reserve fund and add it monthly.