We have three - they are each 2 years apart, but we live in the country in a 2,550 sf home with 6.55 acres of land and 150 acres of logging trails behind our house. We do not "walk" our dogs as we just let them out in the yard with us or we have a 135 foot dog run that we put them out on one at a time first thing in the am and right before bed (or when it is raining so we don't get wet with them - and boy are they quick)
It is an extra expense, and a lot more work - especially at bath time. My husband says never again, but I would do it in a heartbeat, however we will also be going back to two and I won't budge any lower than that.
good luck with your decision, it is also helpful if there is an age gap, I don't know why, but friends of mine with three close in age have many more problems than we do.
PS the website Dan gave is really good, we are waiting a catalog as I don't order on line to get one for our dog run.
Oh - I do take all three by myself to the vet on leashes and they do fine - they are so excited to be going somewhere it is soooo cute, plus they usually grab eachothers leash and walk eachother.