Whether your rack needs the extra posts (doglegs?) or not depends on what you're going to put on it. My panniers have a stiff plastic insert or backing that holds the bag's shape. No dogleg is necessary to keep them from swinging.

What information are you looking for from a bike computer? Basic ones that show current/avg/max speed, odometer, trip distance are pretty cheap. Ones that show cadence, have a large display and back lighting are more expensive, as well as ones that can be mounted on multiple bikes or use multiple tire sizes. Add wireless sensors, GPS, heart rate monitors and they get more expensive still.