I am also a Mother of Twins, so i understand your concern (and jitters).
The best advice that i could give is to get plenty of rest before and after delivery. Eat healthy and make sure you have a good doctor who will understand your concerns. If you're close to your family, recruit them to help you at the time of delivery .. get them to stay at your house for a week or so just so you can get some rest that first week home.
There are also lots of local twins clubs that can help with preparing you for the big day!
Things to have: 2 GOOD SWINGS! My twins spent lots of time in them. That was a huge life saver! Most people think "two of everything", don't spend the money if you don't have to. Borrow stuff from friends who also have small children, you'll be surprised at how willing they are to help out with things like that. Also, make sure you've got some good bottles and a good breast pump (you can rent one too) after they're born. I nursed for 2 weeks, then pumped for 6 weeks after that. I felt like a Cow!! LOL!!
It is hard to do, but with great support anything is possible
Involve your 2 year old.. she will LOVE taking care of those babies. But be prepared for hurt feelings and sadness. The once only child will begin to feel isolated. Make sure when you're in public (since you'll get LOTS of ooosss and ahhhhs), you ALWAYS say.. "Yes, they are twins! And they have such a great BIG SISTER". My boys are still getting lots of unwanted attention because they're twins...
At the time when i was pregnant i also had a 2 year old.. when we brought the twins home he wanted to be a "big boy" and practically potty trained himself!! (things to look forward to).
Join http://www.twinstuff.com/. it's a great message board with all kinds of advise (that you'll need)
Best Advise ever.. Dont give your kids similar names! People will get confused. We considered Jacob & Jackson.. but decided on Brenden & Cole (our oldest has an "A" name.. so we gave them A,B,C names) corny.. i know.. Also, don't dress them the same, they hate that!! It's cute when they're little.. and i did it for awhile, but when people couldn't tell them apart it was frustrating (mine are identical). So I always dressed one in Red & one in Blue, then people knew who was who. To this day they still will (by choice) only wear red & blue.
Giving them names that are not similar will give the kids a sense of individual identity. Try not to call them "The twins". Mine are now 5 and HATE being called that by other people. They are individuals (even though they were born at the same time).
I wish you the best of luck. It's so much fun and I sometimes wish my boys were babies again.. (it was so much easier than listening to them fight) :)
p.s. get one of those shirts that say "YES, THEY'RE TWINS"... you'll be surprised at how often people will ask you, even though it's obvious. After year 5 it gets annoying.. LOL!!
A.