Hiya, my ds was 2.9 when my dd was born, I'll be honest we had a few seriously naughty weeks - about 6 I think. It wasn't nasty jealousy, it was just a huge change, I was desperately trying to get bf going so was parked on the sofa for hours every day and he was bored. He would pee near/ on her stuff, scribble on the walls constantly and generally act up. I wondered where my lovely son had gone! but after 6 weeks it got better and they were ok after that. My friends didn't have the same experience as me so maybe that's just my son for you! Just saying expect some acting up, but know that it will pass.
It's a good idea to keep a store of "easy" snack foods in that you can just open and give to your toddler, cereal bars, cartons of juice, fruit, raisins, crackers etc.
In the early weeks it's an idea to have a box of small stuff like stocking fillers for when you're tired, stuck to the sofa and they're bored. Just things like a new book, puzzle, bubbles, a little helicopter toy, a wiggly balloon, whatever. You could even make them special gifts "from the baby" to help generate good feeling towards him/her. Just pull one out when you need to.
And try to enlist them as your special helper who has the special job of fetching the wipes, and praise/ reward for even the smallest good behaviour towards the baby.
Can he do any hours at pre-school or with a childminder? That time was precious to me, I used to set an alarm and dive into bed with baby.
Will post more but being dived on!!