Have you ever seen 4 year olds play soccer? "The goal is that way!" is about the only coaching you get to do!
Seriously, our coach had a couple of fun games. She had one where they all had a soccer ball and one person had to try to get he flags out of their waistband. While the kids ran around (the field about 1/8 the size of a regular field) they had to dribble the ball. She also had them take turns making goals.
B. They won't criticize your coaching skills. They'll just be happy someone else said they'd do it. The goal at this age is to get them on the field, kicking a ball and understanding that they are supposed to try and get it in the goal. That's a lot at 4 years old.
C. They kids do not play on a full field. It's more like 1/4 the size of a full field. Our coach would wear flip flops and could pretty much walk with the kids as they ran down the field.
D. Our practices were no more than an hour. You could feed her before you leave and probably be fin.
Not trying to talk you into it. Just wanted to address your concerns.