This is what I use to prevent water spots on my opti coat:
http://www.autogeek.net/deluxe-filter-system.html
Also use opti clean and opti quick detail.
Just put the new opti glass on but not enough experience in rain to give a verdict. Little bottle appears to be able to do 3-4 windshields:
http://www.autogeek.net/optimum-opti-glass-coating.html