Correct. The Green/Yellow is the center tap but since many new production transformers don’t have a center tap on the filament secondary, we create the artificial center tap with the 100Ω resistors.

As far as wattage, I like to stay at 1W for safety. Typically, I use 1W throughout the build as they are quieter, except in places where more wattage is called for (ie the power supply ceramics). The kit we supply uses 1W throughout to reduce the overall noise.