Do we want one more?

Being a first time mom was hard and emotional but I knew I wanted two kids. We waited until my oldest would be four and she turned four a couple weeks before her brother was born. After he was born almost 14 months ago my husband and I realized that we maybe wanted one more. I'm going to be 31 in September and really don't want to wait much longer if we are going to have one more baby. If we start trying in September (wanting a June baby because I'm a teacher) we would have a 5, 2 and baby. My question is how did you know you wanted 3? Did you want 2 and change your mind? My oldest was potty trained before #2 how did potty training go with baby?