Do you really have to go with the seat post rack? You'd be much happier with a full rack if you've got a place to attach it.

You might want fenders at some point, but that can probably wait.

If you plan to actually use the Cateye headlight (as opposed to having it for emergencies), I recommend getting two sets of rechargeable batteries and a good charger. The claimed battery life is really high, but it gets noticeably dimmer after about 4 hours. I keep one set of batteries in the light and another in the charger and switch them every couple of days.