I would leave all other dogs at home when collecting.
Bring the puppy home on the passengers lap with newspaper, towel and vet bed if cold.
If you can bedding from the breeder to let your dogs get used to the smell before you bring the puppy home (May be too late for this now) also to help the puppy feel comfortable in your house.
Se aside the next few weeks to socialise socalise and socalise. As you know you will need to go gently with a collie and be prepared to back away if things are too much. But you will have to get out and about every day for the next few weeks.
Visit the vet - often
Sit and watch the traffic
Meet as many people as you can - there does not have to be interaction just meet as many different people, old people, people in hats, young people, men wheel chairs, buggys , crying babies, laughing people, loud people still people umbrellas, walking frames etc
Go to a school and watch from a distance
Sit outside cafes, pubs
Walk with livestock
Go on a bus
Go to the train station
Farmers markets
Teaching to relax in busy environments
Watch noises introduce to gently bangs, rustles of bags, birds (reward no reaction to bird noise, loud lorries dustcarts etc)
and of course basic training.........you have a busy and fun few weeks ahead please lets see some pictures
Change things in your house eg put the ironing board upside down, move your dust bins etc Collies can get freaked by the smallest change so get them used to change and how to react to it
Love the name 