Yes, you need to call for the fantasmic package, it's not available online.
As for whether it is worth it or not: if you plan on eating a TS meal at HS anyway, then it is DEFINITELY worth it. You still need to get there at least a half hour before showtime, but you won't need to wait in that long line waiting to get in the theater.
Fantasmic is great (I think the greatest show at WDW), and should definitely be seen at lease once.
If you weren't planning on a TS at HS anyway, then just wait on line for Fantasmic. If you get on line an hour before show time, you'll get a very good seat (so, you're saving a half hour if you get the package).
As for where to eat: I've never been to Mama Melrose, so I can't help you there. Hollywood and Vine was good, and Brown Derby is very good (but 2 TS credits).