FIRST - CONGRATS!!!

Then:
1) Advice from one mother of twins, my sister, to me when I was pregnant with MY twins: Don't buy anything that converts into something else, you won't have the extra hand to convert. So don't get a swing that turns into a baby seat, get a baby seat AND a swing. This turned out to be very good advice.
2) Hers went full-term, but that is exceptional. Be prepared for premature delivery. I didn't take any of the childbirth classes, Lamaze or whatever, so when I did go into labor at 7 months (my first children) I didn't have any "tricks" to try, my (now X2B) didn't know what I needed, and so on. Get into those classes early, you might miss them otherwise.
3) If a practitioner tells you Take It Easy - GO TO BED. I "took it easy" in my mind and found out later that if I had stayed in bed, Tim's sac wouldn't have ruptured at 27 weeks. BE MORE CAREFUL than you think you'd have to be, or than you were with other pregnancies (I don't know if this is your first or not).
4) My X2B just turned 50 (I'm not 40 yet) but that had nothing to do with our breaking up, so don't worry about your age, you are at a great age to be a dad. You will have a lot more patience with them than you would have had at 30, chances are, and children are very good at recalibrating for other problems. For instance, I have a very bad back, and my kids were trained from an early age to climb up onto furniture if they want to be picked up, or to JUMP when I hold their arms, so that it is their muscles that pick them up, not mine. And they know to be quiet so my Mom can take a nap when we visit, even if they themselves aren't napping.

5) And last: When they are small and you have had no sleep and cannot stand it any more and want to bash their teeny heads together, which will happen even if you only had one, USE THE SOCIAL SUPPORT that is widely available, just look at this thread. We used to take ours to the Mall when we got frustrated, and 17 people would swarm around going Oh honey, you must work so HARD! How do you do it? and so on... not to mention the other 17 who are twins, have twins, have twin siblings or parents or relatives or something... and in about 2 mn you feel right back on top of the world. You don't get this kind of reaction with singletons (who ever went up to a baby and cooed Ooh, my father was a baby once!), so although you get smiles and all, with twins you get a lot of attention right when you need it.

Also: many companies give twin discounts, all you have to do is ask. When buying one car seat say I have twins, give me the second at half-price and this is where we'll buy the cribs. They often will do it even if they have no set policy, just chat up the manager and talk about all the stuff your wee ones will need, and wouldn't it be nice if you had a favorite store...

Not advice, just a note: Mine are fraternal twins, as are my sister's, and I would sometimes dress them the same and sometimes differently. My favorite thing when it was up to me was to dress them similarly but not identically - both in purple shirts but one says Pennsylvania and the other, Philadelphia, or something, UNLESS I was taking them to something crowded. Even now (they just turned 5)I try to dress them as brightly and as identically as they will put up with when going to a crowded and outdoor event, for my own peace of mind when looking around for them. This was very helpful once when Tim got lost at an outdoor wedding and I was able to walk around with Wil and say Anybody seen a kid who looks just like this? And we found Tim in no time. I had tried earlier just by description and the same person who knew where he was when shown the model had just denied all knowledge of small blond curls in a striped turtleneck.

You are in for the ride of your lives, and it will be GREAT!