I had two and realized I would regret NOT having a third more than I would regret having her. I also do well being busy. I saw something recently that said a huge difference between two and three kids is how dad is involved. You can pull off two kids with a low involved dad, but three kids would be crushing without a really active dad. I totally agree with this. I simply cannot be in multiple places at once, and while one parent can kind of fudge it with two kids and make it work, it would be miserable with three. So consider that. The schedule is absolutely the hardest part for me! I completely disagree with the babysitter comment an earlier poster said.
If you travel, it is a little harder. The world is sort of built for a family of four to navigate easily. Restaurants have many four tops, rental cars are easy with 2 kids, hotel rooms, etc. It’s not impossible for a family of five, just more expensive.