Trenchard was a complete visionary. Not only did he figure the transient nature of the aircraft of the day and decided to put his cash into reasonable airfields he also, because of the depression after WW 1 and the consequent constraints on defence spending, decided rather than junking complete trades like they have done since the 1980s he would run each trade down to the minimum he could get away with. Result? Following the decision to expand he had the trades, and instructors, on hand which meant that the RAF manpower, as well as hard infrastructure, could be expanded relatively easily.
The Lutyens design was not confined to the UK
Quite. A couple of weeks ago I visited the RNZAF museum at Wigram (free entry and a very creditable museum). Most of the ex RNZAF base is now a housing estate but many of the buildings remain. And they are instantly recognisable, as is the base layout, for anybody who has been in the RAF.