Just watching a warhammer film club/Jordan sorcery interview with Rick Priestley just now.
@Michael Stockin don't know if you have watched it. At around 12 minutes in he mentions that he created the 'Warhammer world' (obvs with a healthy dose of parody with Hal's input) on 'that general feel of middle European gothick quality and hammer horror/house of horror... It was that standard trope.... And that old Peter Cushing vibe.. ''
He then later says he created it to be germanic (black forest vibe, castle on hill, werewolves in forest), so Empire = germanic. Then says the later guys (ie WHFRP supplements) took & made the Empire to be literally too German. Other 'grim' influences were from film: the devils - Oliver read,the warlord- Charlton heston, the lost valley - Michael Caine...
Rick Priestley on influences on 40k