I agree with truman. Just ride what you have and see how you want or need it customized. There's no point to blowing money if you don't have to.
Before I changed the gear hub, I'd install fenders and a rack, then purchase a decent bag to hang on the rack. But, those are my "must-haves." You'll discover your own by riding and noting what really bugs you. After riding for 3 months, I changed my seat and stem. The Brooks saddle is super comfortable now that it's broke in and the longer stem allowed for a more comfortable commute -- couldn't move the seat back any further and needed a tad more room.
Very happy to hear of a new commuter. Welcome!