Actually, I wouldn't even be thinking of upgrades until I'd at least put about 200-500 miles on the bike. There's a real good chance you'll get used to the current saddle. Everyone complains of a uncomfortable saddle out of the box. Depending on what kind of weather you'll be riding in i.e. rain and wet... I think fenders, a rack and an solid trunk bag can take you a long way. The following aren't upgrades, but would be advisable to carry with you... spare tubes, patch kit, tire levers, multi-tool and a pump.