Water penetration, ice daming, convince me the time has come to seek out
a roofing job.

Access to the very limited attic space is quite difficult. So improving
ventilation and insulation might not be an option. Concentrating on the
exterior what options should I look for to better assure a leak free
roof job?

As a matter for consideration the lot is heavily wooded and shaded. So
much so that moss appears in several places on the roof.