Hello Solomon,A few tips I have for you would be to first; Analyze Deals Properly – Use the 1% rule (monthly rent ≥ 1% of purchase price) and calculate cap rate, cash flow, and ROI before buying. 

They are not cheap.

For example, my bank will sign off on pretty much anything I want to buy with 10 percent down, with a fixed rate at prime, for 5 to 7 years, with a 30 year amortization schedule.

Head over to bank rate or and take a look at the mortgage calculators, plug in the numbers and get an idea of what the property needs to generate to satisfy the intended debt.You still have to underwrite the deal for the non-finance expenses as well(typically 40-50% of the gross rents). 

Totally ok if you don't plan to take any capital out as interest rates are likely higher than your original loan, and it sounds like the deal will cash flow, but just wanted to point that out so you are speaking the same language. 

If you pay cash for something and are able to refinance at a rate that makes sense to pay off your HELOC, that's the only thing I could see making some sense. 

They work well in areas with steady rental demand like suburban neighborhoods or cities with strong job markets​​.Considerations: Your property management needs will be lower, but rents may rise more slowly over time compared to short-term options.Short-Term Rentals: High Risk, High RewardAdvantages: Short-term rentals can generate significantly higher nightly rates, especially in vacation destinations.

If you're $400 below market rate I'd give them chance to "catch up".

Quote from @Brandon Bell: I've owned a property for four years with a standard fixed-rate mortgage, and now I'm looking to convert it into a rental.

What am I missing (besides in some instances you have a lower interest rate but do not get clean title to a property)?