About rats. Like wolves, they have a bad reputation. You say, "Lazy, garbage-eating and self-serving." Hey, people eat garbage if they're hungry enough. And lazy? - few animals move as fast or are as industrious as rats. "Self-serving"? That's a human trait - no animal would understand it.
I happen to own two rats, Holly and Twink. They are intelligent, affectionate, and hard-working. They keep themselves as clean as my cats, and they relish fresh greens and grapes along with their regular feed.
So there. (If I weren't in character as a professor, I'd stick my tongue out, but that would be childish, right...? heh)
I wonder... did JKR give Sirius and Lupin their names before or after she gave them their animals? Because of course the names really telegraphed the animals! I gotta agree about the stag, though. I'm glad James got into trouble as a student, or I wouldn't be able to stand him!
Snape... Feel sorry for him? I dunno. I always wonder why he can't keep his hair clean.
Your argument for Sirius being in Gryffindor is a good one!
Just out of curiosity... why are you swabbing floors?
Do find a pic of Gabriel Byrne. He's got a strong-boned, long-nosed face with deepset haunted eyes.