I also think that the name "Discount Window Cleaning" doesn't quite fit the bill. OK if you're selling goods cheaply then yes you can use the word "discount". But to my mind I can't see it applying to a service because there's no benchmark as to how much a particular service should cost. Eg: Some hookers charge £25 for their services whereas others charge £100 (not that I'm an expert in such matters you understand

), and some window cleaners charge £10ph and others £50ph.
So really when providing a service it's how much the provider values his/her time that reflects the end price. In other words to provide a "discounted" service you'd have to be cheaper than the cheapest w/c in your area.
Anyway that aside I really think you're over-complicating a pretty straightforward business, you:
Arrive at customers house
Clean windows
Collect there and then or leave sae
Return after agreed interval
Clean windows
Collect there and then or leave sae
Return after agreed interval
etc
etc
This is not rocket science and you certainly don't need more hardware/software than mission control at NASA.