Nah, just guidelines, and the Homburg or Bowler might well be way too much, they would be for me! You could get the same effect with a Fedora with modest taper and a full brim. Grey and brown are good conservative choices that go with a lot of colors.
I have a prominent lantern jaw and square face, so your site suggests a round crown and brim (thus the bowler or Homburg). Funny though, the historical examples of folks that have worn either don't seem to fit that description.
Neither Stan Laurel or Oliver Hardy (Bowler) had square faces and neither did Winston Churchill (Homburg).