If youre going in the summertime it might be harder to get a hostel but I have been there twice and never stayed at a hostel, you can stay at these bed and breckfast type places which are around the ramblas, basically it is like a hostel because you share a bathroom but you get your own room and it is usually cheaper. I would stay on la rambla it is centrally located to everything. MACBA, the university ledges is close enough to skate to and Sants is a skateable distance. The whole city is pretty easy to get around