Thirskman,
From experience the smaller villages can be quite lucrative as they seldom see a window cleaner and are more inclined to pay over the odds for one.
As for stepping on other WCers toes, well if they don't already have the houses you get, who are you hurting? There are more windows than there are Window Cleaners.
I will not bid on houses that already have a WCer on principle, the home owners that tell you that there present guy charges them X amount and want to know if you will beat it aren't worth bothering with anyway. You'll soon know if the area already has a WCer as you won't get much take up, residential customers are usually pretty loyal.
Hope this Helps and good luck
Denzle