Don't tell them you clean in the rain unless they pull you about it, most customers wont even realise
this or care unless you bring it to their attention.
Its the same as telling them you might get some spotting on a first clean, it only causes them to check for
something they would have never noticed otherwise.
As for letting them know about your other services have a few leaflets with space at the bottom where you can write
a quote.
If while cleaning their windows you notice their fascia and gutters need cleaned then price it, write it
on the leaflet and post it while your there.
For online payments and so on I think its best to talk to them personally.