Start with your other gear, then get the pack that fits. If possible, take your gear to the store and load the pack to see how it feels. That is of course if you are buying a pack new. Since you are a self-proclaimed newbie, I would suggest that you get some used packs. many forums have for sale sections where you can get almost new packs for a fraction of the retail price. Try it out and if it doesn't work for you, sell it on a forum for close to what you paid. You will likely only eat the shipping cost. Almost all of my current packs I bought used (one still had the tags on it). A lot of people buy stuff and either use it once or not at all and will sell it for pennies ont he dollar.