Congratulations on your twins!!!
I have mono/di twins as well who are 21 months old and a son who is soon to be 5.
There is so much to think of when you get the news, isn't there?
: First a couple of reassurances -- well, you don't need double the clothes of everything (and in the early days, when poop explodes and spit up is every where, who will care if they are wearing their big brother's clothes?) I read something that said 1.5 the amount you'd have with one and that seems about right, especially if you have your own washer and dryer.
One of the first thoughts I had after getting news was "well, there go my hopes for a low-key, no-intervention birth" I had been hoping for after my son's birth (which sounds a lot like your first birth -- long back labor, went from 4 to 10 in an HOUR after they started epidural, 3.5 hours of pushing before using forceps to turn him and his 97th percentile head...). But it sounds like you have a decent care provider -- and it's great she's experienced with multiples -- and that can make all the difference. If Twin A is head down, you should be fine -- after A is born, B is going to move around whatever position he/she is in, and an experienced OB will be able to help get B out if A made her/his way already. I also had to deliver in an operating room (with a good dozen bystanders), but by the time it was time to push, I didn't care where I was -- I was just so excited and ready to go!
And even though it wasn't the birth I had envisioned when the second line turned pink -- it was an awesome birth. I was able to FEEL and control the pushing so much more, and it was incredible. After K was born (she had been vertex for most of the pregnancy), to see my OB (who I had gotten to know VERY well by that point) smile at me and say "she's beautiful -- are you ready to do it again?" was just amazing... and then to get a second one! (sure, she was a double footling breech extraction, which wasn't something I'd do every day, but 37 week old twins were a thousand times easier to deliver than my large-headed, poorly-positioned son).
Sounds like you're already heading in a good direction. Good luck with your pregnancy, eat lots of protein and drink lots of water, and ask any question that might cross your mind.