My kids are 7, 6, 3 and 1. If you can handle three kids, you can handle four. For me, my last baby was the easiest transition. She just fit right in and the kids LOVE her. No sibling rivalry or jealousy. She is their baby. I agree with you about the concerns with giving to them emotionally. Children need one on one time with their parents, I think more now than in past generations. Here is how we do it...
Oldest gets her one on one time after all the other kids have gone to bed, from 8-8:30pm. Second oldest gets his time after he gets home from Kindergarten and the younger two go down for a nap from 1-1:30. Younger brother gets his time when younger sister naps in the morning and the 1 year old gets one on one when the 3 year old is in preschool. We also take them off alone to do things while the other parent stays home. I take my oldest to baby showers and to plays and take the younger ones out to the store one on one. My husband takes one for errands, then out for ice cream or hot cocoa. He has also taken the oldest son camping twice and my oldest daughter accompanied him on a business trip once.
We also do family dates every Saturday, (museums, festivals, parades, service projects, parks, sledding, etc.) attend Church and stay together on Sunday (no work commitments or playdates) and family night on Mondays. (Family night includes singing, praying, lessons of morals / values, family council, calander planning, fun game or activity and treats.) The kids take turns with us conducting the meeting, giving the lessons, picking the activity and preparing the treats - with help from mom and dad, of course. It is one of the best things we do during the week with our family.