A.J.
You shouldn't punish him for wetting the bed. His bladder isn't even developed enough to last very long without going potty. If he wakes up in the middle of the night, you should just gently tell him its time to try to go potty and help him sit there and try. Put a nightlight in the bathroom so you don't have to turn on the big light so hopefully he doesn't wake up too much. I would just keep a pullup on him for now at night. My daughter is 3 1/2 and still doesn't stay dry all night long. Some kids just take awhile to develop the muscles necessary for that.
As for being gentle, have him practice on a baby doll. Let him practice holding the baby doll, feeding it, touching it gently, etc. And let him hold the real baby with your help on the couch. Show him how to play with a baby. Let him help you by fetching diapers or wipes or a burp cloth. Let him pick out the babys clothes sometimes. Make him feel like this is his baby too and get him as involved as possible. And don't worry about him hurting the baby. Poking the babys head won't hurt, even the soft spot. You have to push pretty hard to hurt the baby ther =) just make sure you are always there to supervise until he learbs and always try to give him a job to do so he isn't just trying to mess with the baby all the time.
I also nursed my 2nd baby and my older one was just 2 yrs old when she was born. I would just sit on the livingroom floor with a few pillows to nurse the baby so I could still interact with my older one. (I knew I was a pro when I could change my 2 yr olds diaper while nursing lol)
I promise it will get easier, but it might be slow going at first. Just relax and enjoy both your kids and don't worry so much about the small things =) congrats on your new addition by the way!