hi paul,
yes, suggest you join your local club. there are some excellent clubs in your area.
as to what loco if you ask a group of model engineers you will get 20+ different answers!
i dont think there is any need to build a stationary engine first. i certainly didnt when i started my first 5"g loco at the age of 16 with no engineering training or background.
size and type of loco is rather determined by cost and size of available lathe to turn the wheels, and complexity of the boiler. i would avoid anything wih a tapered barrel and belpaire firebox and piston valves for a first attempt. that still leaves a huge variety of available well known designs. there are some to avoid unless you want to do a lot of research and corrections. also depends what type of loco you fancy… something Victorian with lots of shiny brass, something with a tender, something freelance or something based on an actual fullsize type.
when you go to a preserved railway what are the locos that you particularly like?
there is also something to be said for choosing a loco that has a construction series available either in book form or don young's magazines LLAS or ME etc. have a look at the Reeves online catalogue as a starter.
cheers,
julian