same as above, do your research first. it's not as easy as it might seem, window cleaning. difficult to self motivate, keep customers happy, work in all weathers, and run the business well.
however, get it right, and if window cleaning is for you, then it could be the best move you can make. but it will take time, and commitment.
as for vans, transit connect are popular, or Peugeot expert or equivalent. I have Volkswagen caddy, payload 750kg, I can have about 400 litres water on board legally.