How often should I change brake cables and housing?
I encourage replacing once there is a noticeable decline in performance (usually that means that they get "sticky").

Depending on the type of elements you go through, you might get back most of the perf by pulling the cable most of the way out, adding a drop of thin oil, then sliding the cable back through all the housing. Repeat a couple of times wiping cable each time. This will often clear the bits of gunk that are making it sticky.

Changing shift cables/tape at same time:
Tape...absolutely, it's cheap and I always feel like I've treated my bike nice when it's sporting new wrap.

Shift cables...if they are in good shape and the drive train is clicking along nicely, I tend not to mess with it. If they are getting sluggish like the breaks, then I'd go ahead. Keep in mind on the shift cables that they will stretch a bit so you will need to tighten the cable and possibly do a slight retune of the drive train a bit after a few days.