That sounds like a lot of fun for you and Finn! I don't have a lot of advice to add, as it seems to me you have gotten really good advice from those who have responded already

I will add that I got my RB collie, Cody, when he was 9 months old, and he had never been exposed to stairs before! He was terrified of the deck stairs and wouldn't go up or down without a lot of encouragement and help at first. We just had to do it the same way as introducing a new puppy to stairs until he gained confidence and soon was zipping up and down like a pro