I agree that collies need a job to do but they do not need hours and hours of exercise. They do need brain work.
Too much exercise and you will have a very fit collie that just needs more and more exercise but can still be very uptight etc
A collie that is worked or given brain work will be tired relaxed and chilled.
Re socialisation go very carefully with collies if your dog is showing a reaction to other dogs make sure that you are meeting calm, social dogs. Control all greetings with other dogs to dogs that you know.Do not let collies think for themselves that some dogs can be worrying - you will have a reactive collie in no time.
If you are going to puppy socialisation classes be very very very careful with a collie pup, many collies will find the rough and tumble of labs, retrievers etc bundling together to be way too much.
Collies will live off adrenalin so you need to make sure that adrenalin levels do not get too high. If they are ball chasers do not let them chase balls for hours and hours - the collies will want to but it will just make them way to hyper. You can hide the ball and get them to track it but keep activities calm.
Throw away your food bowls and make the collies work for all their food, tricks, scattering food, activity toys etc.