I let the APs auto manage their tx power. Aerohive firmware does a decent job of not running wide open when it doesn't need to. I also have 1 AP per floor to get adequate coverage.
My cable modem doesn't have Wi-Fi. I turned it off on my router since it's in the basement and there's a dedicated AP down there.
Walnut Creek and infomagic saved me so much headache. Can't beat the bandwidth of a FedEx truck, especially when you're 28.8 at home.