Get your pack last, figure out the gear that suits you then take the gear with you to a store and try out several packs. Packs are like shoes, what works for one doesn't mean it will work for you. It also good to know your torso length before you go in.

Try your gear in your back yard or car camping first. This way if a item doesn't work for you you either substitute it for something else.

Good luck and enjoy your trips.

Oh and welcome to backpacking.net!