J.S.
K.,
I have 4 girls, the youngest turned 4 months old yesterday. I agree with Amy that it seems people expect bringing home a sibling to be this big problem, and I really don't think it is. Having brought home 3 younger siblings, I've never really experienced regression, lashing out, or other bad behavior from any of my girls.
I have offered dolls to all my girls around 2 years old, and only one of them has really been very interested. With my oldest I gave her a set of dress up shoes, clip on earrings and a necklace at the hospital when she came to see her sister, and she was thrilled with those, but haven't done any gifts since then. We let our kids know all through the pregnancy that God is sending us a gift of a new brother or sister, and they are involved with the pregnancy and have always been excited for the baby to arrive. I've been "late" every pregnancy, so the questions, "Will the baby come TODAY?!?" get old!
As far as dad helping, if you plan to breastfeed then he needs to realize that you'll be busy for about 15 minutes every 2 hours, and he WILL need to help your oldest, because putting her off over and over will cause problems and is just not fair to her whether there's a new baby around or not. Also, you should be basically in bed for the first week, so you'll need him to do the housework and change baby diapers and outfits, too. If you don't take that time to heal right away the whole process will be drawn out much longer.
Finally, as Amy also said, redirecting is for daycares who aren't allowed to discipline. At nearly 3 years old, you're about a year late with time outs or spankings. She needs to be told immediately that hitting is never allowed, ever, and if she hits she will be (insert specific punishment here). Then follow through every time. If she harasses another kid, then she is punished for being mean to someone. The minute she sees her baby, you talk with her about how baby can't do anything for herself and it's our job to feed her, change her, and protect her. It's her job as a big sister to show love to her baby and protect her and when she gets bigger, to teach her the right way to do everything. Stressing the protector/teacher role will go a long way in welcoming baby to the family and avoiding problems.
Blessings on your journey!