We also had that issue with several properties that had a lot of cash flow in the spreadsheet but not as much in reality, and have optimized our portfolio now to focus only on locations with high rent and value appreciation.

I like the idea of value adds, but ADUs are not an optimal path.

They have been long-distance self-managing but it seems like they haven't been able to fully optimize the rental income. 

By built correctly I am referring to SEO (search engine optimization), and the website programming.

.- diversification - better chances of optimizing your results in terms of risk, cash flow and growth- Taxes.

I feel buying and holding a rental managed by a property manager in the IRA could have a higher yield, but one would not be able to use deprecation to their advantage, so one year flips make more sense (instead of 1031 exchanges for tax optimization).   

Are you marketing it like a professional listing and is the listing fully optimized with professional pictures, title, description, etc?

Evaluate the rental market in your area to determine the optimal configuration for maximizing rental income.The choice between using cash flow from your current house to cover expenses or pay off the mortgage faster depends on your long-term financial goals and risk tolerance.

However, installation costs and procedures may vary, so it's worth getting quotes from both if you're not doing the work yourself.As a hard money lender specializing in fix and flip deals, I've seen successful investors use a mix of these sources to optimize their budgets while maintaining quality.

Typically over 5+ units 25% down is optimal but 20% is possible..I don't think I'd recommend a property management company for your search, likely a multi family focused investor RE broker and strong nationwide lender.