Thanks everyone for taking the time to reply.
Kevspainter: Thanks. I'll have a look at Edgar Payne's work. Yes, I will post my finished effort - as long as it's not too frightful!
marcdalessio: Practice does seem to be key to most things, that's a valid point. I'm certainly going to work through the process a few times before I even think of starting the commissioned piece.
LarrySeiler, artistinmemphis and Davkin: Thanks for bringing Rungius to my attention - an excellent painter, and also very colourful work, which I like. To enlarge from 11x14 to 90x120 is quite a daunting prospect!