I have 4. DS's aged 12, 10, 7, and DD 6.
I think having them close together is chaotic, but it's only for few years. I feel we have just moved out of the baby years (in that baby toys are gone, no change bag, then can toilet and dress themselves, we no longer need complicated equipment) and it seems to have flown by. I'm so glad I had them close together rather that spread out.
You get into a pattern. If you change one nappy, you may as well do two at the same time. Snacks for 2 or 3 take very little longer than snacks for 1. When feeding the baby, the other two are close enough in age to enjoy the same story.
A 3rd child (and subsequent) just fit in with the household, Especially when school/nursery starts. You have all the clothes and equipment ready to go.
Cars, 3 car seats can be squeezed in, we did it. Depends on the car and the seats, but you can put one in the front and an adult in the back.
Rooms. In old house it was bunk beds and cot/toddler bed for the boys in the largest bedroom, the then baby was in with us.
New house is 4 bed. For ages we had big two in one room, little two in the other and a guest room.
Recently put 12 year old in his own room with a high sleeper with a double futon sofa underneath it, for guests. He gets kicked out when guests stay. Other two boys have the larger room. DD gets the smallest room (we have the master!)