You need enough housing to go from the shifter then along the h-bar, under the bar tape, then a wrap to the front housing stop, with enough to allow the h-bar to turn better then 90 degrees. Than another section from the rear stop to the top of the brake. Cables are generally a front or a rear in length, the rear is longer. Then you need housing cutters and cable cutters, if you don’t have either I’d just have the shop do it.

I’d also do the fronts as well, as you’ll have the bar tape off the bars so might was well do both. I like the Shimano all-in-one kits, but have also used bulk housing.