My son was 3 years and one month when my daughter was born. I had read somewhere that it is a good idea to buy a gift for the older sibling to give to him from the new baby when he first meets him/her. My son fell in love with my daughter after that. He is sweet anyways, but it made it a definite positive to get a gift from her on a day that was all about her and I.
I stay home and run an in home daycare, a home photo gifts biz, and an local support organization that I founded for Parents in my county. Currently I am trying to expand it and create chapters in other counties. Oh did I mention I also homeschool.
A few things that are important are that you don't rely on him all the time to help you take care of the baby. He will enjoy being a helper some of the time, just not full time. Set aside time for each child to have individual time with you and/or your spouse.
The biggest challenge I have is staying organized, on a schedule, and focused. Make daily to do lists. Commit long and short term goals on paper. Make sure not to get to busy to play with your kids. These times are only here once, don't miss them. Delegate some things to your spouse.
Don't forget you time. Don't overdue it, and don't forget it. Pamper you. Participate in your hobbies, include the kids if you need to.
Enjoy it!