relax, you'll have until it leaks to fix it!
looks like the basics are covered in your questions.
http://www.ehow.com/how_9347_hire-ro...ontractor.html
in buffalo ny they require tearoffs and allow only one layer of
shingles.
let your roofer decide when to do it he may have expensive leaking jobs
he'd prefer to clear first. wait for warmer weather unless the attic or
crawl space is showing problems.
spending money on a properly pitched new rain gutter system to get the
water away from the house is important. sounds like you think the last
guy did a nice job, maybe look him up again?