I have never worked at 60ft but 30ft i have and at that height i am approx 10 ft away from the building, on other occassions i am less than 5ft away at that height due to main road.
When its windy and going to 30ft its ok, just rest your pole on the building as you are going up.
As for explaining to customers this is the easy bit and its best to be totally honest with them, dont promise everything will be ok on 1st clean. Yes sometimes it is but sometimes it is not. As for telling them 3-4 cleans everything will be ok, it can take alot less or alot more, if you have been using fairy i will tell you now it will take longer. If you are one of the lucky ones that use GG3 or GG4 then you should be fairly fine with them all, you might get the odd one.
Hope that helps
Justin
Ps I did place my how to use a wfp on this site but it got removed for some reason. Try
http://www.squeakyclean4u.com/wfp/wfp.PDF i need to update it abit, but it will help