Will old Apple Watch models work with AirPower

According to a support article from Apple the Apple Watch Series 2 has a Bluetooth 4.0 chip. So common bluetooth headphones should also work with the Watch.

The Apple Watch Series 3 GPS + Cellular has LTE built-in. Here are the bands supported by the USA version:

LTE
2 (1900 MHz)
4 (AWS)
5 (850 MHz)
12 (700 MHz)
13 (700c MHz)
17 (700b MHz)
18 (800 MHz)
19 (800 MHz)
25 (1900 MHz)
26 (800 MHz)
41 (TD 2500)

UMTS
800 MHz
850 MHz
1700 MHz
1900 MHz

SOURCE

That same page also lists the bands for other countries.