Backpacks are going to fit everyone a little different. Best bet is to try several on and see what you like. Personally, if you haven't done it before I'd go to a good outfitter and get fitted. You'll need a large/Tall frame pack to help with your height and girth. I'm 6' but my torso size is long so a taller pack fits my fame better and puts the waist belt where it should be.
On a personal note, Arcteryx packs are my favorite and a cheap intro into the backpacking world is the USMC Surplus ILBE packs. They can be had at surplus stores or eBay for about $100 or so. Just make sure to look for one with the lid, hipbelt and shoulder harness all included. It is heavy but well made and you can cut a lot of excess stuff off of it to drop 2lbs off the pack. There are pleny of youTube videos that explain the packs in detail. The packs are made by Propper but designed by Arcteryx. They are a great value.