I had a spinal fusion about 12 years ago. I can't remember the details of which vertebrae though... It was so long ago I can't remember much about it, but I do remember the pain and discomfort in the following few months. However, there have been no long-term affects. Flying and driving make me uncomfortable after a while, but I've no problems with heavy landings (not when i'm flying of course...) or with aeros. My back is a bit sensitive to the touch, but that's more psychological than physical. I would imagine that medical science has improved a fair amount since I had my op, and would guess you will have a good chance of little in the way of long-term problems.
.... and I always win the 'biggest scar' competitions.
You might want to try and contact someone who teaches Alexander Technique and get them to advise you on your posture. Play around with your chair until it's comfortable and take frequent short breaks. Try raising the back legs a little or the front, or putting some kind of padding behind your back. Also, try the Scoliosis Association UK. Although they're aimed towards people with spinal curvature, they often have useful advice on post-operative solutions.
Good luck and let us know how you get on.
