its time consuming mate. if your not confident get someone who is.
windows are easily scratched when cement is present. dont scraper off cement, try and wet it off as much as you can and be careful. get some sticky label remover Tygris do a good one.
CHECK ALL THE WINDOWS FIRST BEFORE YOU START FOR SCRATCHES so YOU are not liable.
as far as money goes. you may get 3 - 4 done a day. your looking at around 3 - 4 days work in my opinion. (depending on the state theyre in)
if it was me. if there is 10 window on the house, i would usually charge £10. builders clean i would charge for outs, £10, then in another £10 and another £10 for the time youll be there. £30 a house. £540 for the lot
£550 for you trouble
hope this helps