I want to add a ridge vent to my existing roof, architectural shingles are about nine years old: is this the way to go??

It's okay to a add ridge vent to your architectural shingles, but I do hope that you have the warranty from your contractors if something were to happen. It is fine, actually. It would look more appealing if you installed one. Next time, however, ask your contractor about your warranty first, just so you can be sure to be able to get your money back before you pursue what it is you’re planning.

Yes, and there's no other venting that's better. Just make sure you have soffit intake-vents to start with and that you close-off any gable or other roof exhausting vents or the ridge vent won't do much of anything.