My philosophy is to wait to buy accessories so as to discourage and prevent GAS. Yes, accessories may cost more than the camera - all the more reason to not buy them unless you need (or really want) specific ones.
Luckily, Bay I accessories are relatively cheap. On the other hand, Rolleinars and filters for my Bay III are quite steep.
I have both Rolleinars 1 and 2, but I find that I use the 2 more than the 1. My uses do not indicate or justify a Rolleinar 3. YMMV.
Accessories you are more likely to use (assuming B&W) are the typical colored filters. I have yellow, orange, and red.