Thanks for your suggestion! I've added ringed planets as a unique host-shape. As for asteroid belts: It's a request that's come up before, but I'm still thinking of the best way to implement them.
Two things to note though: You can delete hosts with the trash can icon, which is a bit cleaner than setting their sizes to 1. You can also adjust the line width of all orbits in the settings menu (though you can't further adjust the individual orbit thickness other than selecting their shape)