(example: repaint, bathroom, kitchen, doors/fixtures etc.)I want to only put in about 10k.Thank you for sharing your time and experience!

I dont do a total repaint every time I turn over a unit, I only do a full repaint under extreme conditions (last on was due to pet urine smells in the house).It usually take me 2-3hrs to clean the place.  

Repainted the entire house ourselves, enclosed one room with French doors to make a 5th BR or office, changed all the ceiling fans, door knobs to brushed nickel, added an above stove microwave.

Had to turn it over and scope of work was similar to yours, however I used real tile, brand new fridge, new toilet, repainted the entire home and cleaned top to bottom 5,400 out the door.  

Turned out not only had the corporate executive known about a flat roof leak into floor ductwork...huge mess...and not disclosed it, he had the damage repainted to disguise it.

One of my investor friends painted his HUGE duplex bright 'oops paint' blue because the city insisted he paint it or get cited.But definitely not as bad as this one that was repainted this year & for some reason has not sold YET!!!.

I also would not entertain a tenant wanting to paint a unit /have it painted anything more than my standard neutral color that I use on all my units.What you are trying to avoid is (a) a tenant dictating the color of your paint, only to move out 3 months later, (b) a tenant asking for and being granted an "improvement"; this sets expectations moving forward, (c) any cost to you for any of this stuff.If a tenant wanted a unit REPAINTED (it would be my standard color), I would calculate the cost of materials/labor, do the math and notify the tenant that you would be happy to paint their unit, but it will cost "$x" which would require a rental increase of "$y". 

Repaint walls something other than white, maybe a nice grey or another color someone suggest. 5.

4) Walls: Have you experimented using different material to cover walls, rather than just having to repaint nearly each turnover?!

@Greg Scully gave great options to increase the value of your property, just adding a fresh layer of paint can instantly make the house look much newer.Replacing/repainting the door and adding window shutters also adds a lot of value to the exterior of the property.