Weight has less impact than spine-spine is everything; also don't have a preconceived notion about shaft length-that will be adjusted later in the tuning process. What's the string type, and what is the make of the bow-do you know the degree of centershot? That is likely the most important bit of information to have when selecting shafts.
Also, get the shafting, feathers, and all the other arrow stuff from a sponsor here, and use that 'big outdoor store' for lawn chairs and canoes.