Some need new furnaces, flooring, and paint.

There is no given answer here, because the whole property needs to be relatively consistent.Kitchens and baths are the common answer, but if they are passable and you choose to invest in them anyways at the expense of peeling paint (or off putting exterior color) and overgrown landscaping, the appraiser and tenant will be walking up with a bad taste in their mouth, thereby not valuing the interior work you have done.But think about the general flow of someone looking to rent: more bedrooms will typically dictate more rent.  

In my area, they actually require a little more than the local municipality and lately have been especially strict on cracked paint because they were recently sued and lost.

Until he wasn't.Sometimes people change due to pressures we don't see, and sometimes people are just like m&ms . . . dark on the inside with pretty painted shells. 

Bought under assessed value, slight value add through cosmetic rehab (paint, light fixtures, flooring) What was the outcome?

As for turn over cost I would save for new floors and paint obviously every house is different if you have a 30 year old oven then add that in to but as a rule of thumb save for paint and new floors.

And I may get multiple bids for the same work, like multiple paint bids, multiple roof bids, multiple flooring bids, etc.

., same tile, paint, flooring, etc.

Just recently I undertook to do some significant painting at two of the buildings and my wife offered to help me out.

Floors will get stained and refinished   Back yard and front yard will get freshened up along with a coat of paint for the facade.Budget is 20k