Just FWIW, as mentioned to browse some of the articles about lightening up, but I strongly suggest you put together the rest of your gear *before* buying your pack if possible. Otherwise you are buying a giant pack just to fill it, as opposed to sitting down, making a list of what you really do need, seeing how much it weighs and what volume you need, then finding a pack that both fits you and works to carry what you will be carrying.

So rather than saying "I think I need lots of volume" - put your gear together and ask yourself "why".