Hi
Welcome to the Forum
Hopefully, you'll have found some interesting topics already here which will help with a lot of your initial tasks starting up - canvassing and leaflets etc.
The most accurate way of judging the potential market is to start knocking on doors and asking and, of course, driving round and seeing how clean peoples windows are!
We already supply window cleaners in that area so, unfortunately, it's not going to be an entirely 'open door' but, that said, there are often large housing and industrial estates that get overlooked!
Good luck with it!
Mike Boxall