Bangor is mainly students so its very English dominant you won't ahve any promblemsthere, its Caernarfon and the villages that are predominantly Welsh speaking.
I had a look at the BBC website and thats probably the best resource out there if you cant go to actual classes. If you do have the time over summer check out welsh classes all along the north wales coast, they do an intensive two week summer school which i believe is the beginners course im doing weekly.