You will want to interview at least a couple of realtors and determine what resources they have available for you in several arenas (lenders, contractors, more). 

How did you determine that? 

What criteria do investors use to determine if a seller financed deal is good?

Understanding your top priorities can help in determining whether Stessa, Baselane, or another tool might best fit your needs.If you're comfortable with apartments.co for rent collection but want higher yields on your cash (this is me reading between the lines) you could have the transfers go into a high yield business account like BlueVine 1.5% interest or something like CapitalOne 3.9%.

Obviously the numbers and location would determine which is the best option for me but these would be my preferred methods. 

Might have a tenant that will sign a ten year lease and drop some money into the space.

Rent payments from the medical LLC are fully deductible as a business expense, while the property-owning LLC will report the rent as taxable income, which can be offset by deductions for expenses like mortgage interest, property taxes, maintenance, and depreciation.To ensure compliance, document how FMV was determined—using market comparisons, an appraisal, or similar data—and draft a formal lease agreement outlining the terms, rent amount, and responsibilities.

From my understanding, as long as you intend on doing a STR when you close, there are no rules against changing your strategy after closing, especially if you find that something else is more profitable.So in our case, the lender determined an STR would bring in ~$3500/month (with all of their conservative factors), but now that we operate it as a huge 3300 sqft Co-Living property, it actually brings in $7000/month.

When you have a duplex and tenants on both sides stay for ten years, it almost guarantees that something isn't right.I would study your market and determine the value of your rental, because I bet you are losing money every month.

LTV would be determined by the type of loan.