I either want to convert half of the property into airbnb (8 rooms downstairs for airbnb), and the other half (8 rooms upstairs) for longer term tenants, or either the whole property as airbnb.

I can’t believe you found one half empty unless it’s a declining neighborhood. 

My listings have only been active for about a week and a half.

Keeping half in the business ($17,500) to reinvest is smart.

It’s the easiest way to get into more expensive markets such as Atlanta.Keep saving.

I’m considering selling it and selling my primary residence to build a duplex where I’ll live in half and rent half. 

Seems like about half the population has pets these days, so by NOT allowing them, you are cutting potential bookings by half - maybe more, since a pet owner is more likely to go STR versus hotel.

Beyond that, certainly any money that's made they're going to be entitled to half of it, regardless of what you spend. 

Some duplex units are set up as zero lot line properties where instead of owning one unit in a 2-unit condo association and the condo assoc. owns the building, you actually own your half of the building and land. 

That half bathroom added ~$50k of value per the comps (mission beach, 3 units from the ocean).