I have some theories on who's what symbol on Bill Ciphers wheel.
Well first of all you need to realise that only one symbol per character. If you have seen the episode dreamscapers (s1 e19) you would know that bill cipher calls Mabel "Shooting star", He calls Dipper "Pine Tree" and he calls Soos "Question Mark". So you have them figured out already.
Stan would be the claw for what's on his hat, Wendy I would say is the bag of ice, which most people would say as well because she's around bags of ice a lot or cool stuff, also because she's a "cool person", you also have one wrong in my opinion, you could be right but I have a theory that the hand is not for the author, but it could be, but I think that it's for a secret society in Gravity Falls. Everyone in the show has four fingers, that would be normal for the cartoon characters, but the journal has 6 fingers on it. That's one more than an average human, so you need to look out for the characters that have 5 fingers, one more than the average cartoon character. Some of those people would be: Stan, Soos, Lil Gideon, Deputy Durland, Lazy Susan, Old man McGucket and so on. If you play the Rumble McSkirmish game on the disney website it talks about a secret society. I think that those people could be in it.
The love heart is obvs Robbie, I think that Llama is Pacifica Northwest because if you look at the llama on mabels sweater it points the opposite way to what it does on the wheel. Those two are enemies so they point opposite ways. The star is gideon and the glasses are stanleys. Some people say that stan pines has a secret twin and some say that it's just him in the past. If you look at stans glasses now they dont look like the ones from the cipher wheel, but if you look at him when he was younger the glasses match the wheel.
These are my theories, they may not be right but it's what I think.