In emacs C-g cancels any command that has begun. Is there a similar solution in tmux for after you have pressed Ctrl-b? I thought about researching this by hitting lots of keys but that would only make this worse.
You can use any key that is not bound to anything. From what I see in the man page Ctrl-g is in fact *not* bound to anything (in regular mode) so you can use it after Ctrl-b.
If you want to explicitly bind this noop functionality to Ctrl-g key, you can do it by placing something like this in tmux.conf:
bind C-g run 'true'