Cable Housing for Friction/ 4 vs 5mm
 

With bar end shifter friction set up, can I use the same housing for brake and shifters? 4mm? 5mm?

You can use brake housing for both. Do not use shift housing for brake.

You can but, I could locally find a Jagwire (quality isn't bad) shift & brake cable set, complete with ferrules, ends, etc, for about 15 dollars after tax.

The cost for my 25' of brake housing was 20 bucks after tax.

Therefore, I'm not sure if you would save any money, or maybe you are looking for a colored cables?

I buy housing by the roll and keep most colors in my inventory of tools and parts. I'd suggest getting a few feet of the color you like of the 5mm housing, and buy stainless-steel cables.

But that leaves a slight problem: Do you have good, bicycle-specific, cable-cutters? And get some end-caps to crimp on the ends of the cables once they are installed and cut to the proper length.