I'm trying my hand at making stats for a deity in D&D 3.5 (god of music, if it makes a difference) using the rules given in Deities and Demigods. So far everything makes sense except one thing: I can't tell whether or not his maximum number of class levels is supposed to be connected to his divine rank. Is there any sort of officially-stated correlation between the two, or should I just assume 40 or so levels like most core D&D deities seem to have?
There's no connection.
Deities and Demigods has a vague suggestion in the footnote on page 26:
And that's it.
Just add as many class levels as you feel necessary to represent the "mortal" abilities of the deity.