My friend was one of 4 under 18 months (parents adopted 2 ethiopian orphans as they were 'sterile', only to find out a month after adopting the last one that they were preggy with twins - awesome fam photos with 2 dark children and 2 blonde haired, blue eyed kids!) and although they were quite well off so had nannies etc, her mum always said that the best thing about it was it was like a wee play group every day. The kids entertained themselves as they were, and still are, the best of friends.
One of the things her mum did say was the best piece of advice was try and get into a routine so there is separate time for each child as even though they are close in age, they will need to experience things separately. And also, like other people said, a good support network will give you a great advantage for the tough times.
I know things haven't been easy (and clearly from the posts tonight you've copped a lot of flack for it - not that I'm saying it's all one-sided as I haven't been here while it was happening) but the main thing is, you will have 2 kiddies with a year apart, you will do your best and so will you DF. And that's all anyone can ask for, so I say good luck and I look forward to hearing about your *hopefully* non-eventful, non-MS pregnancy!