Wait...
"Take it seriously and base it on what is in the comics"
You ARE aware that Captain Marvel was a comedy comic book before DC integrated him into their continuity, aren't you? It was never "serious" until DC tried to modernize him in the past 15 years or so.
This was a guy who had a WORM as his arch-foe.
The old comics are quite funny, so I see no reason to try to make a "serious" Captain Marvel/SHAZAM! film. I'd think it would be much better to be true to the origins of the character and make it an action-comedy... Cast Patrick Warburton, and go with it.
Just like I would hate to see a "serious" Plastic Man movie. That would suck. (but if they do cast Plastic Man, it should be Bruce Campbell)