Oh, as far as the relationship between otters and Jack Russell terriers, apparently the dogs are known for chasing otters? That's what I've read elsewhere.
It really does seem to me that everyone's Patronus represents them in some way.
Otters, like <PERSON>'s, are clever (they use tools like rocks to break into their food and can handle puzzles) and inquisitive. Clearly that's pretty suitable for <PERSON>!
Luna's is a rabbit, which has a host of sybolism. In Japan it's associated with the moon (like her name); one source says that in Kerry, hares were thought to hold the souls of the villagers' grandmothers, and <PERSON> could be said to be an old soul; they're a symbol of fertility and new beginnings, and the "new beginnings" part seems to fall very much in line with her personality somehow; and finally, rabbits are born with their eyes open so superstition says they hold powers over the evil eye, and of <PERSON> it could be said that her eyes are more open than others', both to the creatures she believes in which nobody else does, and to the nature of the people and the world. She's pretty aware. So I'd say her <PERSON> is really fitting, as well.
<PERSON>'s is/was a horse, and horses are thought of as spirited and free, which matches her personality. I can't find it now that I'm looking, but I read once a superstition that said, "because horses can find their way in the dark, people believed they could foresee danger or could guide souls through the underworld." If I tried I could probably spin together something about how she "found her way through the dark" time that she was under <PERSON>'s diary's control to become the confident person she later was, and that she "became a guide" to <PERSON> in his own dark times by becoming one of his closest friends and then his wife.
<PERSON>'s is easy enough: Not only does his family seem to have some kind of affinity with wolves (assumed because of their names), but because of his condition and the way it's treated in the wizarding world, it is pretty clear that his werewolfishness is something which causes him some great consternation. 247
He resents it, but he can't separate it from his personality as a whole; to him, the werewolf is who he ultimately is, and what he's a slave to. To his mind, it's not only a representation of himself, but also his entire history and maybe his fate.
I do not even know what is up with the <PERSON> family. <PERSON>'s Patronus was a stag before he knew that his dad was an animagus, so it was independent of that information - but was <PERSON>'s Patronus a stag before or after he could turn into one? Was <PERSON>'s Patronus a doe before or only after she fell in love with <PERSON>? The <PERSON> family is just hemorrhaging deer, it's crazy. Deer are agile and difficult to capture, though, which fits with the family's association with <PERSON>... and there's a lot of dignity to a deer in mythology, especially in its association with the forest, as there seems to be much dignity attributed to the <PERSON>, as other wizards speak of them. But seriously, this group gives me some trouble.
In general, though, I think it can be said that there is a lot of evidence to support a person's Patronus being a reflection of some intrinsic part of their character or personality. It's that way with a large enough sampling of the characters with known Patronuses to feel like a pretty good bet. 247