I have a great relationship with my primary lender and they require at least 20% down.

Key Principles:Mindset and Goals:Think Long-Term: Real estate is a long term play in most cases Set Clear Goals: Define your financial goals and how real estate fits into your overall plan.Finding the Right Property:Location, Location, Location: Invest in areas with strong economic fundamentals, good schools, and low crime rates.Cash Flow is King: Look for properties that generate positive cash flow (rental income exceeds expenses).Consider Appreciation: While cash flow is primary, also consider properties in areas with potential for long-term appreciation.Financing:Get Pre-Approved: Get pre-approved for a mortgage before you start looking at properties.Leverage Wisely: Use leverage (debt) to your advantage, but don't overextend yourself.Consider Creative Financing: Explore options like seller financing or partnerships.Building Your Team:Real Estate Agent: Find an experienced agent who specializes in investment properties.Property Manager: Consider hiring a property manager to handle day-to-day operations.Accountant: An accountant can help you with tax planning and financial management.Attorney: Consult an attorney for legal advice and contract reviews.Managing Your Investment:Maintain the Property: Keep your property in good condition to attract and retain quality tenants.Screen Tenants Carefully: Conduct thorough background checks on potential tenants.Review Your Finances Regularly: Track your income and expenses and make adjustments as needed.Example Action Steps:Set Your Goals: Define your financial goals and how real estate will help you achieve them.Educate Yourself: Read books and articles about real estate investing.

and pays rent in their primary.

I was applying for a DSCR on my rental property (cash out refinance) and everything seemed ok, my FICO 680, DSCR 1.08, Appraisal $179K, LTV 65%.Unfortunately, the lender cannot close due to derogatory on record on my primary residence.

I've had a conundrum the last few years since I bought my first primary residence, I was lucky to get a good interest rate <5% When I purchased this property I was very green and new to real estate but I had heard or seen somewhere on some financial blog or podcast that if you pay an extra $100/mo toward your mortgage in many cases you can accelerate your payoff date 5+ years.

If I rent out my current primary residence, I could generate over $1K in positive cash flow, so I'm considering moving into the rental property and handling the repairs at a more manageable pace.

TLDR: a bad idea for your primary home, a really bad idea for your LtR and an incredible horrible idea for a STR.

This way you could get an FHA loan and rent out the primary residence. 

Doing this like a brrrr I see as the best bet, for example my property does still have room for improvement adding a bedroom and bath to the primary structure and then the ADU.

Process of selling primary residence, but instead of investing in another property, we are looking at purchase a small business instead.