The thing that worries me with 4 is having to have more rooms in the house, a bigger car and then the school runs, homework and activities for 4 kids just seems daunting.
We have a 3br house and 4 kids and it works OK (while they are young they'd happily all sleep in one room). We are doing a renovation to get an extra bedroom though. We did have to get a bigger car but that's a relatively small thing to deal with. Our kids go to local schools so the school/daycare run takes 25 mins from leaving home to arriving at work. They'll all go to the same school for a couple of years then the high school is an easy walk from home.
Mine don't have a lot of homework (yet) so they usually do it at the kitchen table while I make dinner. I do limit after school activities, partly because I often have to take all of the other kids along, partly because I think that one or two activities is enough extra (the school provides a lot of optional activities directly after school as well as optional music lessons during school hours so that's a big bonus too and they can do as many of those as they want).
Bearing in mind my age (30) if I did have 4 they would be close together in age (maybe 2 years apart max or maybe a set of twins in there if we were lucky).
I was very lucky as my first was born just before I turned 35. Having them all close in age has a lot of positives, the biggest is that they are all interested in the same sorts of things so it's not hard to find activities and outings that they all enjoy. The downside is that four little kids can make a lot of work, especially when they are sick or cranky.
I am a lot more organised with day-to-day stuff than I was before kids. Cooking, basic cleaning and laundry fall into a daily routine that I have to stick to (once I get behind it's hard to catch up).
If I'd started my family younger I might now be thinking about another child or two as my littlies are 3.5 and getting more independent, I love having a full and busy house. I couldn't have managed any more little kids before now though
I never imagined having four kids. After #1 I was adamant that I wasn't going to have more than 2. By the time #2 was 6 months old I was keen to have another one and lucky enough to eventually have twins.