The thing baout the Muppets from a design standpont is that Jim Henson dealt with abstarct forms and very simple geometric shapes. So many of the Muppets (unless desginated, frog, bear, pig, dog, etc.) are just that abstract forms. Even early on, as many around here will tell you, Kermit was just an abstract. it wasn't until Don Sahlin (the late great puppet builder) came along and decided Kermit looked like a frog that Kermit became a frog. So to answer most of your questions, Maynard....
Gonzo is an abstraction. He was created originally as a kind of monster for a TV Special special called "The Great Snata Clause Switch" where he was simply known as the Cigar-box frackle. And was pulled out of storage and named "Gonzo" for the Muppet Show where he was termed a 'whatever'.
Rowlf the Dog is a dog. And if you want the specific breed of dog, they make reference to him being a hound dog in "Dog City" and I believe they mention that somewhere else too.
Dr. Teeth is again just an abstract human. Although, you are right here baout basing a character in a real person. Dr. Teeth is actually based on Louisiana Blues Artist, Mac Rebbenac (aka Dr. John) If you ever see Blues Brothers 2000 Dr. John sings the song "Season of the Witch" just as they arrive at Queen Moussett's. He's also one of the jeyboard players in the Louisiana Gator boys. That's him in the white suit and large hat just to the right of the drummer. The one who look a little like Dr. Teeth....you can't miss him.
Snuffy's full name is Aloysius Snuffleupagus and he is a...Snuffleupagus. it's a made up animal like Fraggles, and doozers, but on Sesame Street. However the Sesame writers have done a marvelous job over the years of putting together a sort of Snuffleupagus culture, if you will. Apparently, Suflleupagus's are native to Hawaii, eat cabbage and every year celebrate a Snuffle festival where they dance the Snuffle hula. Marty Robinson once said the Snuffle-hula was one of the hardest things he's had to do as a puppeteer. It involved a long dance down Sesame Street that he had to do over and over and they wanted it without very few cutaways. it was exhausting!!
Scooter is a another abstracted humanoid. Athough many people here will refer to him as gopher. it's actually a go-fer. it's an old stage term referring to the fact that his job was to "go fer" coffee or "go fer" sandwhiches.
Animal the jury's kind of out on this one. Many people will maintain that Animal is some sort of monster, but I and a few others believe that Animal's species is "drummer". I tihnk I've seen a few Henson designs and so forth that claim that but can't remember where. I always thought it was a funny idea though.
And I tihnk Big Bird is just that, a big bird, but if you want to put him in a specific category than OK, I guess you could say he's a large canary.
hope tihs tries to answer soem of you questoins. I agree with you that many artist do base their creations on people around them, but the key thing there is not every character is based on someone and when it is it's no neccessarily someone famous or another chracter on television or movies. The world would be a very dull place if we every show featured characters based on characters from other shows don't you think? A lot of times (particularly in the Muppets) a character emerges from some bit of business that the puppeteers are doing or because of an interesting design or because of a need to filll a certain void within the cast.
But if you're looking for characters based on certain things here are a few you may find interesting, Maynard....
Pepe the Prawn is based on Bill Baretta's aunt from Madrid who often times used the word "ok" as a question.
Scooter is based very strongly on Richeard Hunt when he first joined the Muppets because he was always so eager.
the Two-headed Monster on Sesame Streetcame from seomthign that puppeteers Richard hint and Jerry Nelson had been doing one day on the set. A character was based around it.
the Flying Zucchini Brothers are actually based on a waiters from a restaurant where the Muppet show writing staff like to eat. the food was good, but the service was lousy. IN fact the service was os lousy, it was amusing. The Muppet writers based a cannonball act on it.
Oscar the Grouch was laos based ona waiter who had once served Jim Henson and Muppet writer Jerry Juhl at a restaurant names "Oscar's" Apparently, the guy ws just mean. later Carroll Spinney based the voice on a taxi cab driver who drove him to work one morning.
Again, I hope that kind of fills some things in for you and helps out. It's really just a bit if intersting trivia.
--Matt