Well I only have two children (18mnths and 3yrs), but I run my own business from home and would consider a 3rd.
Basically are you asking the choice between having 3 kids and working for someone else or working for yourself. Or, just having 3 kids and and working for yourself versus having 3 kids and working for yourself? I would imagine that 2-3 isn't that big a transition, I'd think the most huge transition, is going from 0 to 1 as far as babies/kids are concerned. Once you've got a couple you've already got no life anyway ;-) diminished expectations, etc.
I have childminder/nanny (what's the actual difference?) 9-2 3 days a week, then I work weekend mornings, with help of husband, and work evenings too, but not every evening.
If you're in a creative industry I think it's harder not to do it than to do it, that's what it's like for me. The balance is a juggle for sure, but I'd loose my mind if I didn't satisfy my creativity/business.
I'll preface this with saying I only have 2 kids though, and I just cannot quite decide about 3. I'm one of 3, so 2 seems like a bit of a lame effort, but then again, I'm enjoying the fact that I've for the first time in 3 years, got no bottles to wash and, hardly any broken nights, and the thought of going back to square one with a newborn....
I'm watching with interest.