We've got twin boys approaching 2 and a 4 year old daughter, nothing much to add to the above really.
The first 6 to 18 months have been hell, despite the fact that they generally slept well, having the older one too has made it hard as she craves the attention, if these are your first then great, enjoy them!
Now they're walking and communicating more they're getting easier and do play together a lot, although they do tend to egg each other on to mischief.
Definitely second the routine thing, although it doesn't suit everyone's personalities (if you're not used to routine/are disorganised!). it can seem harsh but in our experience it generally makes the children happier if they have a routine and you also generally know that they're getting grumpy because they're tired/hungry. I would advocate Gina Ford, but not religiously, get the book, take what you need and see how it works.
With regards to buggies, we got a mountain buggy twin with the twin carrycot (pick one up cheap on ebay if you can) for when they were smaller which was great, the buggy is ideal now, robust and easy to push but can be a pain in small shops etc but any twin buggy would.
Also, as mentioned above, get two toys the same, the fights over toys can get vicious.
Also second "double trouble" and "you've got your hands full there", drives me potty, can't people be more imaginative?!