You'll have no trouble Quandram - there's plenty Irish pubs just off the Ramblas which would be the best in terms of atmosphere, you'll find them no problem, as well as a dedicated sports bar about half way down the Ramblas on the right(it's orange on the outside and says Sports Bar, beside a subway. It has loads of screens showing about 10 different sports channels at once - altho most of the area is taken up by tables so its not so much of a standing bar.
There will always be spare seats for the Barcelona games - when I was there in September we trotted up on the night and got some tickets for the Lyon Champs League game for £30.
If you are planning on going, I'd suggest 2 things. a) watch out for touts outside the ground who pick out tourists that are only there for one game - they'll tell you a load of bollocks about how the tickets are sold out but how they can sell you some. They hover right beside the bit where you actually buy tickets (a kind of beige/grey cabin with lots of little windows that ticket people are behind) so just march past them and go straight to the holes in the wall.
b) Pay a bit more for a slightly higher category of seat(altho this really depends whether you want to be up with the gods, as it is an amazing sight. That aside, its full of tourists there for one game, certainly not a football crowd and virtually no natives there, just a bunch of twats with their ronaldinho replicas on clicking away on their cameras every two seconds who will annoy you.
We were up there for the Lyon game but had pre-purchased some tickets for the 50th anniversary sevilla game - atmosphere was soo much better as we were in with the locals and not far from the nutters behind the goal.
So depends whether you want atmosphere or great views!
Pricier seats:
Cheap seats: