I've already renovated one of the bathrooms, and I’m planning to paint the interior, update the kitchen cabinets, possibly sand the wood floors, build a fence is a corner lot and increase the rent for the room since my tenant is currently renting the entire 3-bedroom, 2-bathroom house for $800 a month.

Not that I don’t enjoy dealing with tenants, maintenance, lawn care, Home Depot and Lowe’s trips and tenant change overs (I recently put new carpets, kitchen floor, appliances, vanity and mirror in the bathroom and fresh paint in my upstairs unit).

Typically, since I'm well connected because of flipping, HVAC, roofers, lawn care, carpenters, kitchen & bath & plumbers and electrical all are good sources.

Large basement and attic space, new roof and some of the kitchen is already torn out from the current owner. one bedroom does have a closet that will need built. plumbing seems fine, maybe a couple angle stops to change.

You can get some estimates from contractors for what they charge for big ticket items like to renovate a bathroom, renovate a kitchen, replace the furnace, replace the roof, etc.All wholesale deals should have free and clear title and you should be able to see the sales agreement before submitting the earnest money deposit.

When it comes to AirBnB I have found its location, number of beds then amenities like kitchens and outdoor spaces that attract quality guests and demand higher prices. 

Meaning you may be able to do some cosmetic or smaller renovations like bathrooms or kitchens in your duplex when the tenants turn over and those smaller investments can demand higher rents, so in the longterm you may have more cashflow from the duplex to help fund a future investment in another property while you wait for market conditions to change.

They will try to run 2 kitchens and that can mean clogged drains in your wet bar kitchen.Be sure there is personal recourse when you need to sue them for $40k in repairs above the deposit.

Quote from @Dean Malka: 1) what's your range for remodeling a kitchen completely (granit, backsplash, tiles, etc)?

Plenty of things in kitchen so people don't need to wonder if they can make XYZ in there.Once you get it all setup, it should go pretty smooth.