We have 3 dd's - 7.5, 6 and 7mths. 'Tis early days, but so far absolutely lovely! I just didn't feel 'finished' with 2, and although it seemed a bit mad, as we had got through the baby stage and everyone was settled, I felt like I wanted to mix it up a bit, and it has. I feel that it has changed the dynamic of the family in a good way. The older two are very close (sometimes love/hate) and having the baby has broken that up a bit - they both love 'their' baby and give her loads of energy. She loves her sisters and is looking for them when she hears their voices and gives them huge smiles. I also think that it brings us closer as a family because we all adore her.
I feel like I am really enjoying the baby stage this time around, because of the age gap the older two are at school so I have some time to spend with her, and also I feel more confident and experienced.
When I am on my own with them, having to divide attention can be difficult, but I can leave the older two to get on with it to a degree, and you also work out ways of managing (eg bathing baby when older two are having a 20 min stint on computer, etc).
Going out and about is a bit more of a palava, but not much different to trying to get out of the door with two.
So far she has cost us nothing other than nappies, because we have all the equipement and clothes. It will be more expensive in terms of me working only 3 days per week, and paying for nursery.
For holidays, we mostly do homeswaps, which are fabulous - don't have to pay for accomodation and can self cater as much as you like - just have to pay to get there. Air fares to visit my parents will be more expensive.
Basically, we all think it has been a really good thing and are glad we did it. (btw - that 'not finished' feeling has gone away)