I have three cats,, and they are all good with the small animals!!!
I have a cockatiel, and fish, and used to have a guniea pig. Angel actually tries to play with Snikkers our bird. She doesn't try to hurt him,, she just wants to play with him. They have soft claws, so she tries to put her paws in his cage,, but we have all the opening tied down so she can't get into the cage. Honestly Snikkers gets mad at the cats if they don't pay attention to him. He sits and squaks and throws a heck of a fit until one of them pays him attention.
Also snikkers was a resident bird,, he's been with us for a year before we got Angel and Chestnut and now Kella. So he warmed up to them within a good month!! The fish aren't bothered becuase we have a lid on them. and the gp,, well they were scared of him, because he would jump around. My neice took our gp because she begged my husband!! Now the big dog,, that's a whole nother story,, we have a rotti/lab mix and she is scared to death of the cats!! It's kind of funny, but they are still working on the whole bonding!!!
Good luck!! Once you get a cat,, you'll be soo happy!!!