Ah, you'll be fine, newborns sleep so much you'll have plenty of time for DC1, especially in the first few weeks. I was worried that DD would be jealous of DS (she was 23 months when he was born) but considering how boring he seemed to her, she couldn't have cared less about him! She was a bit cross with me for leaving her when I was in hospital (stayed three nights) but that was the worst part. Just make sure DC understands they're not going to have an instant playmate, explain how babies are quite boring and sleep a lot.
Make sure you're not holding the baby when you first see DC, have someone else there to hold him/her or make use of car seat/moses basket. Have your arms free to cuddle DC.
I would get any visitors to make a fuss of DC1, but not to ask the obvious "what's it like being a big brother/sister" or other baby questions, probably best to stick to everyday things e.g "Wow! What's this toy, can you show me how it works?" If they bring a gift for baby hopefully any with two or more kids will also bring a gift for older child, if not perhaps prepare a few little presents for them, that you can keep hidden for such occasions.
Have meals that you can all eat in the freezer. And make sure you have quick snacks available for DC.
Get some new books from the library so you can read something to DC while feeding baby.
Definitely agree with getting used to feeding on the floor :-) also don't worry if baby has short and frequent feeds. It makes it easier to fit in with older DC and the baby will get used to it, they'll still get all they need.
As for bathtime etc, you wont really need to worry about that for a few weeks as new baby wont need a bath for a while. Try to keep to DC's normal routine, I found putting DS in his car seat was a trusted way of keeping him quiet/asleep/safe while we bathed DD.
And finally, ask people to help you!! I found lots of friends stayed away for a while to let us find our feet, but I know they all would have helped if I'd asked :-)
I've rambled on for ages, sorry!.....Now does any one have any tips for DC3???.....