Can't help you on the breakfast, an Irish breakfast is just an English breakfast with some gross pudding.
The only remotely metal place I went to was called Dice Bar, in Smithfield. It's more of an alternative bar, but with a fairly dark atmosphere. I'd say you'll be pretty shit out of luck on that front, unfortunately, unless you can time your visit with a good gig going on at Whelans or The Academy.
You can do touristy Dublin stuff in a full day, more or less - the city is really quite small. If you want to see more of the countryside, especially on the west, I'd say your best bet would be to book a day-trip to the Cliffs of Moher via Galway. Galway was probably my favorite city in the country (largely circumstantial, I had friends there), and really does have a great nightlife if you wanted to book a night out there as well. It's more of a college town than Dublin, and I felt that the crowd going out was younger and less "done-up"/metropolitan.
You could also VERY easily (via the DART train) take a day trip down to Wicklow national park or something south of Dublin. Glendalough wouldn't be a bad choice, nor would Brae/Greystones. If you're into hiking, there's a Brae to Greystone hike that's great, and a very long, gorgeous one at Glendalough as well.
For a ridiculous night out, look into Harcourt St - I might not remember my nights at Dicey's or Copper Face Jack's, but I definitely won't forget them.