The only approach I’ve found effective is offering a deposit alternative, which lowers upfront costs for tenants without devaluing your property.

The house has appraised for $335k, my hard money note is for $242k, and I'm looking at only about $15k out once closing costs, taxes, and insurance are accounted for.

Having a vacancy costs money!

Our average monthly revenue is $2,675.We have had 46 stays so, $4,600 in cleaning fees (the cleaning fees are included in the avg $2,675 monthly revenue) If we have someone clean it, it costs $100.  

If it costs $100,000 to install an ADU and it rents for $1,000 a month, then it may be worth it.

While this can maximize leverage and ROI, challenges include getting lender approval for seller financing, high carrying costs, and the pressure of short-term loans.

That's pretty low for a 3-BR - I'm seeing the FMR for a 3BR in that zip code is $1,850.But at $1,300 for rent, you'll probably find HMLs that may lend you around $120k if you have a good credit score in my opinion, which means you'll need $45k + closing costs.

And after you have sent 15k on downpayment and closing costs, you have 10k left, which is just enough for one HVAC emergency replacement and some paint. 

The family viewed the house, loved it, and requested that I install satellite TV and add it to the costs, which I did.

So, the extra unit may cost you more then it brings if you cannot access equity or if the market discounts the property when you go to sell due to financing available.