We market the property as available now, meaning that it doesn't have to be repaired and/or it is vacant.

The biggest mistake new investors make is to walk a property, maybe explain in general terms what they want and then let the contractor come up with the SoW.For a bedroom this could be:- replace carpet- repair closet dooror- remove carpet- remove curtains, nails and screws- replace closet doors, entry door SKU#- replace window SKU#- refinish hardwood floors 144 sqft, clear/oil-based- prep and paint all woodwork- patch walls, texture, paint walls eggshell white clay, ceiling flat white- replace light fixture SKU#, replace lightswitch w decora/white, replace 3 outlets&covers- install blinds SKU#Obviously, the cost would be quite different.

The buildings are getting older and they don't have the funds to do the repairs.

you mention ARV - what is the cost to repair the property to get it to that ARV?

If I purchase a duplex and live in one side and decide to renovate the side I’m living in. Can I write off/ deduct my expenses for the renovation?I would be doing this to be able to rent it out in the future at a high...

That does not qualify as "managing repairs."

Prepare the property: This is the time to purchase new furniture, restock supplies, and complete any necessary repairs.5.

@Eric CarlstromMy STRs tend to experience more frequent repairs than my long-term rentals so I tend to budget more for repairs and maintenance. 

By the way, the tenant should be charged for this as part of "cleaning and repairs." 

Maximizing Deductions: You can still claim tax deductions (mileage, repairs, management time, etc.) on both properties as long as they’re legitimately related to rental activity, even if one isn’t in an LLC.