I just use a flat 40% of rent as the expense budget, and do not attempt to break out individual items.

I was back end vendor at Rich Dad for a few years and they did a good job of having one meeting then doing detailed break outs in a class room setting without all the Hype like an Armando Montolongo did. 

His development Costs break out like this:1.

Should I break out withholding for general maintenance expenses and capital expenses into different line items and how much as a percentage of rent should each be?

Some people never break out of that "job" mode and build their financial future.

. ;)  There were various breakout groups for different products and systems by others.

@David Faulkner These are spot on how I break out flipping v. wholesaling as well. 

COREE is a group (paid) that has monthly meetings and weekly breakout meetings for members.  

Strive to break out of this cycle..

You need to run the worst case analysis as if rents will never increase and you will not manage the property better than the current owner.So in regards to your breakout, I don't see you accounting for vacancy, property management (regardless if you self manage or not) and Capex (don't know if you included this in repairs but doesn't look like it because that's really low depending on the age and current updates to the property).