I am not very good at it!
Today I had a very helpful chat with Phoenix Precision Paints. Really great customer service and advice. I have now placed my order for:
Grey etch primer (PQ31 kit)
Gloss black for the wheels and frame (P975)
GWR signal red for the buffer beams (P14)
Sable brushes (1/8 and 3/8 flat)
I plan to brush paint the frames and wheels. In reality all steam locomotives were brush painted so I am being authentic here. I will spray or, more likely, have sprayed the superstructure once it has all been assembled and fitted. I may reconsider this if my early efforts go well.
One great piece of advice was to paint a tin can for practice. I am going to force myself to do this.
I have also ordered the book “How (not) to paint a locomotive”. My worry is that I am always good at theory and less good at practice. We shall see.