All these discussions about 'how much' are pretty meaningless because it's all down to trial and error.
Some people can manage with a gentle trickle, others use a mini Niagara - you have to find out what works for you.
I use a 60psi Flojet with no controller or restrictor, I just switch it on and attach the pole hose to the microbore. The water comes out like the above mentioned mini Niagara, but a couple of quick passes and a single zigzag rinse and the job's done.
As to how much per window, I haven't the foggiest, but I do know I need about 200lt for £100 worth of work so I fill the tank accordingly.