As a note, maybe try to avoid inline comments unless formatter is fixed, because autoformatting _will_ misplace them. (Not to mention that imho inline comments in Smalltalk are a result of a bad design��� if you need an inline comment, maybe turn that into actual code).
In any case, there are no guidelines afaik��� otherwise we would have comments everywhere already. :)
Perhaps one thing regarding class comments: There was a push to use PIllar there if you need formatting, but I am not sure what is the current status of that.
Peter