What factors do I need to consider to figure out if a particular set of toppings will work well on risotto?
So risotto is pretty much a blank canvas, much like say rice or pasta. 

So your first concern is simply to pick ingredients that go with each other. For example: tomato &amp; corn risotto, good. Tomato and chocolate risotto: bad. 

Second, you may want to choose a broth, cheese, and optional wine that goes well with your choice of main ingredients. 

Third, because risotto is Italian in origin, the most certain combinations will be those classic Mediterranean flavors. You aren't going to go wrong with say asparagus and olives, or artichokes, peas and lemon. When you start making Thai risottos, you are farther out on a limb.

Finally, much of the pleasure of a risotto is in the rice itself, when properly prepared. That pleasure is fairly delicate in nature, so for maximum enjoyment you should choose reasonably delicate ingredients and/or use them in relatively small quantities.