Mine aren't very detailed because I rarely do any kind of RP, and none seriously.
Q) do you have more than one fursona?
main: Rusty Coyote (Dark Coated Coyote)
secondary: Rusty Fox (Arctic Fox)
goofy one: Huggy Bear
(A purple and green baby fur, lol)
Q) how different are they from one another?
The coyote and fox are very similar in attitude but the coyote has more of one, and a bigger ego. Huggy Bear is purely a goof off fursona I use for silly stuff on Skype and once IRC, lol.. bugs a certain friend of mine to death and its hilarious to RP Huggy Bear.
Q) how similar are each of them to you?
The coyote and fox are very similar to me and are pretty much an extension of my own personality - especially the coyote. Huggy Bear is not like me in the least (as I am not a baby fur) which is what makes that one so fun.
Q) how often do you find your preference switch from fursona to fursona... if you ever do?
Generally the main fursona I have has been a slower switch. Though the AF one as a main only lasted for a few months (after being a Red Fox for years, and before that a couple different Pokémorphs since 1999), and the coyote is recent but the coyote also means the most to me beyond just being a cool character I wanted. The coyote is the first fursona I've had a real attachment to and felt something for.
That about sums it up.