Sharing leases, profit and loss sure but no inspection. 

I was profiting over $20k annually.

If you net a $300,000 profit from the sale of your current you could in theory invest in a $1.5MM property.

We sell the property and each side get their money returned off the top then we split the profits 50/50.

But then again, no one ever went broke paying tax on profit. 

If I add up all the lender fees and my holding costs—like points, origination fees, and interest —I can figure out how much profit I’ll make and what my maximum offer should be.

This is a property has been in the family a long time and I'll be holding onto long term as it turns a good profit.

The rates will be lower and will allow you to maximize profits.

Determine the most likely sales price of the build (factor in the cost of the land also) and include all selling costs to arrive at your net profit and ROI. 

But that also depends on your down payment- putting only around 20-25% down is hard to have a profitable STVR.Ultimately with STR v LTR, I'd be mainly curious about your intended use of the property.