I had my oldest, thirteen months later had twins, and am due with the next when they are thirteen month (4 in 2yrs 2 months). Can honestly say it's not that bad, i'm very busy but they're already great friends (and enemies sometimes!) We had trouble on one wage, but now the twins are here the family assist has gone right up, i'd suggest you ring centrelink if that's a worry as they'll tell you how much extra you'll get.
Upside is there was no jealousy, they all sleep lots during the day so i get a break (like now!), and i always have a happy child to hug!
Down side is it can be hard for me to do things by myself with the kids, but i just do the easy things during the week and leave the hard ones for the weekend when dad is home.
We always wanted lots of kids, but i have lots of things i want to do as well, and this way they're all at school by the time i'm 27-gotta love that!
Kelly, 22, 1 @ 25/1/04, 2 @9/3/05, 1@5/4/06