Re-Shingling on a home of 40 plus years

This is my childhood home where I grew up, and am now am part owner of. I have been told that it's time to replace the roof, and given that I know nothing about this type of thing I am wondering if you could lend some professional advise in this regard.

What is the norm.....? Which way is the best and least expensive to go? I've always been told you don't have to go the cheapest way but take the route that is approximately the middle of the road in expense. So, what do you suggest.

Also, does one have to have the roof stripped down to the basics and start again from scratch (so to speak) or how does that work. I understand that everything would depend on the condition or damage to all of the layers of the roofing materials already in existence, but I just need a basic rule of thumb. Also, would one have the gutters replaced when a new roof is put up?

I thank you for any help that anyone may have to offer.