I totally agree with Sarah about the Deuter III. I love it and I think it's on sale now at REI. I had a kelty and that killed my back. I too had a chunkie baby, so that was a life saver. My son loves the camelback bladder and learned how to drink out of it around 14 mo. It keeps him well hydrated because he loves to play with it and drink from it.
As for sleeping, we've done a couple things. He's slept with dad (I'm the light sleeper), he's slept in a snow bunting suit, and he's slept in a sleeping bag. The problem is that he hates the sleeping bag. I'm really glad I tried out one of my old ones first. Now I'm in the process of making him a quilt. The only way he would sleep in the sleeping bag was if I but the mattress in the bag too so that he could roll over easily. I think I did this when he was about 18 mo., before that he was either with dad or in the snow bunting.
As for diapers, I've done the GDiapers, but the gdiaper covers are horrible. If you really want to go this route, I would get some good quality cloth diaper covers, such as bum genius. Obviously, you can't bury the inserts, but I have thrown them in pit toilets. Now that my son's going through far fewer diapers, I'm just shlepping the dirty diapers.
The only other thing I would recommend is leg warmers. I knit, and made a pair of wool ones for my son, but the cotton ones would work as well. Their pants ride up in the carrier, so it keeps their legs from being exposed. It also keeps them warmer during outdoor diaper changes.
We have been ridiculously fair-weather campers since having our son, so I haven't had to test out rain covers, but I will say that the only one I would trust to keep baby at all dry is the deuter one. REI makes rain pants/jackets for little tykes though. I would go ahead and get a much larger size and just use the velcro adjustments. My son has been using a 4t rain jacket and 3t rain pants since he was in 18 mo size. This I have tested as we use them around the neighborhood for puddle splashing.
For what it's worth. I know this sounds like a lot, but it's a lot easier to take a baby out than it is to take a toddler out. It's good to get used to it now, before they are also running around trying to hug the tree with poison ivy.