For this issue (the error mentioning Serial1), see this post from a bit farther down that thread, which has revised code that should compile OK for you: WifiShield with arduino uno compiling error - #23 by kreggly
Basically because the Arduino Uno doesn’t have a 2nd serial port like the original code was expecting, this revised code disables the serial port typically used for debug and uses it to facilitate communication with the ESP chip.