My first was 5 years older than #2, so quite a different situation that having a toddler, but here goes:
It really helped in the last months of pregnancy to admit that I was scared of having another baby since I wasn't sure I could possibly love someone as much as I loved #1. Of course that turned out to be silly since I was immediately over the moon with #2, but at the time I didn't know it was possible!
I signed #1 up for a "big siblings" class at the hospital and I really liked it and think he benefited from it. It was brief- like one hour. But they each brought a doll and swaddled it, learned about not touching baby's face, learned how baby would give "finger hugs", talked about how much time baby takes to eat and change and rest. #1 has always been the type of kid that appreciates confirmation of information from another source, so having a nurse go over these things worked for us.
My mom stayed for a week after #2 came and, while she helped with laundry and cooking, she really left me alone with #2 to rest. She took #1 out on all kinds of adventures and playdates. I do regret letting her take him home with her (about 6 hours away) for the following week. Before the birth, it sounded perfect: "he can be around and play and see baby, then off he goes to have fun with cousins for a week before really settling into the reality of having a little one around". I ended up feeling like I'd traded him in for a newer model and cried a lot about it (of course with hormones flowing, I was likely to find something else to cry about if I hadn't let him go!)
I never insisted that he throw diapers away or do a ton of other chores related to baby. He wanted to be helpful sometimes and that was great- at other times he wanted to just play around, and that was ok. (Of course, now that he's getting a third sibling, I do expect more!) At that time though, I was wary of him viewing the baby as someone who created a bunch of work for him.
I think the rest of your ?s are more for people who've gone before with littler ones. I could use info from them too since #3 and #4 are going to be the closest in age I've ever had (3.5 yrs apart) and #3 has very much been our baby this whole time!