Boost extends your WiFi for up to 30 meters, direct line of sight. If you have heavy brick walls or a double story how this may reduce the distance

Yes. The free Sengled Boost App allows you to control your light though your smart device. You can dim the light as well as turn it on and off. If you turn the main power source off, the Boost can not extend your WiFi.

The Boost works with 2.4 GHz connections.

Yes, as long as you turn off the light using the Boost app. Since the Boost needs to have a constant power supply in order to extend your Wi-Fi network, using the wall switch to turn the light off, will also cut the power supply to the bulb, causing it to shut off completely.

While it is technically possible to connect one Boost to another, this can cause degradation of your Wi-Fi signal.