Here's a good crash course in roofing and what part the shingles play in the grand scheme of things - they are just protecting the underlying felt which is what keeps the water out of our homes.
I have seen in my utility bills the difference that having the soffit and ridge vents have made. A very quick payback investment if your home does not have them already.
I love big metal drip edging to take the water away from the eave trim of the house.
This would also be a great time to lose the gutters where they are not serving a purpose - splashing onto the siding, or drainage, or any other purpose other than "that's the way we do things here." Some traditions have no real reason for their continued existence. Stop this one if it makes sense to you.
A three tab 20, 25, or 30 year shingle is fine. The Dimensional or Architectural shingle may be more appealing to the eye, but if most of the neighbors have three-tab, go with this one - the material and the protection of your home is the same.
Go with a contractor that does not want any money down, until the job is completed and you and the BigGuy are happy with the job.
Be sure the contractor is liscensed and bonded and is able to give you copies of same.
Your insurance agent should be happy to provide you with the names of several reputable companies that are known to him and who have done good work in your area over a period of time - no fly by nights.
Do not worry about the "this bid is good for ten days" clause - sales gimmick.
Companies with names and numbers of local satisfied customers, with whom you verify same, are a good thing.
I hope some of this helps you guys. ;-)