My last baby was a crazy mover! And I had an anterior placenta. I felt him constantly, he never stopped moving. He's 2 years old and still doesn't ever stop going! I never noticed his movements slow down. You could see my entire belly moving all over the place. My husband just couldn't believe it! He had never ever seen that before! I'm almost 13 weeks pregnant again and I started feeling this one move at 11 weeks. I think it's a good sign that they move. My other 2 worried me because they would have VERY quiet periods that scared me. Never had that happen with my last!
The further along in pregnancy the less "kicks" you'll feel. But because there isn't very much room in there anymore you can feel every movement where as before you only felt the strong ones since they could still hide.
Sounds like my baby! I have occasionally wondered the same things you are. With my son, he moved a lot, but not near as much as my girl has been and I am just over 30 weeks now. She seems to be doing gymnastics in there quite frequently - lol - and I feel like she's a lot bigger than she probably is. I honestly don't know if there's such thing as too much movement, but since my ultrasounds looked good, I just assume everything is OK.