I would carry my dog down stairs until she was about 30 lbs. If I had long wooden stairs I'd carry up and down.
With stairs that long you should carpet them or at a minimum put grip strips on them. Carpet is way better.
I had a dog jump/slide down wooden deck stairs with grip strips and she ended up with TPLO surgery.
When your dog gets fast and crazy at 5 months or so you are going to have to be really careful.