@Grant Baker Case by case and even if you repaint skipping ceilings can save you a bunch of time. 

It collapsed the ceiling on the floor beneath.

And there are some good to have items like granite counter tops, remove popcorn ceiling etc.Total renovation cost would go up to 10k if I were to do all of them but the rent increase I would see from previous rent collected is anywhere from 200 to 250 a month.Now, is there a formula to calculate how much one needs to spend vs rate of return in rents?

We want to remodel, knock down two walls, get rid of the 80’s carpet, popcorn ceiling, new trim.

I'll close on a duplex promptly when I get back and bust through my "14th floor ceiling."

So far we added new efficiency upgrades such as adding Insulation into the attic (None to begin with), caulked all windows and ceiling air vents and weatherized all the doors.

If you shop and ask around, you should be able to find a painter that can do a walls, ceilings and trim for $1/sq ft (paint included), cheaper if the paint scheme is already the same.

We recently had a long term tenant move out of one of our single family homes and she left it absolutely covered in roaches- like falling out of the ceiling covered.

Seal walls, ceilings, doors and trim with Kilz or similar primer.

I just rehabbed a studio that was so bad the tar from smoking was running down the walls lol. we washed them and the untextured ceiling down twice and hit it with oil base primer.