I'm from Dublin so I can tell you the best ones around. Isaacs is one of the hostels with the best reputations in Dublin. I've been inside and it's a really nice hostel, great restaurant too. Very friendly and helpful. They have 10euro beds too so very cheap. If cheaper for any of the hostel sites if you book directly on their site.
Good pubs are Whelans and The Village. There are some great live bands that play all kinds of music in Whelans - it's famous as a live band venue.
Try to stay out of temple bar. Very expensive! Plus in some pubs, they increase the price of a pint after 11, 11.30 etc. Kehoes on South Anne Street off Grafton street is a good pub and popular with locals. It's like being in someones sitting room when you go upstairs. Part of the charm
The main thing...Have fun!!!