One of the major benefits of a KStep, is it combines controller, stepper drives, and 0-10V on the one board. My only complaint is all the IO and 0-10V is on IDC header, so you do need a small BoB to make life easier(about £10 upwards on ebay - search for "16pin IDC breakout board")
As this is a Novamill conversion, space in the cabinet is limited, unless you're willing to alter the cabinet layout. I'd need to measure to check, but I think you should be able to squeeze a KStep into the existing controller space.

Power supply wise, a bridge rectifier and capacitor is all that's needed to get a supply for stepper drivers. I just checked the wiring diagram, and the transformer outputs 28VAC, which should give about 40VDC. I also noticed the diagram shows a 24VDC supply for the control electrics. Not sure why I thought it was 12V...

If you don't want to rely on USB for 5V, you'll need to add in a 5V power supply. I personally use switched mode DIN rail mount ones, as they do the job in a nice compact format. Not the cheapest option, but easy to install.

To give you an idea of how compact the KStep setup is, here's a photo of my prober/CMM control cabinet -

I made my own BoB with what I had lying around, but then I only needed two inputs (EStop and Probe). If I wasn't in a rush to get the machine running at the time, I would of ordered a ready made BoB.
The build thread can be found at http://www.machsupport.com/forum/ind...c,27732.0.html with some info about running it closed loop at the bottom of the first page.