I used to live in Hayden, ID, and used the route you're talking about on our trips to San Diego. The first portion of Hwy 95 you're talking about is mostly single lane in each direction mountain driving with very few passing lanes to let others get by you, or for you to pass a slow truck. Coming into Lewiston the descent is steep and the road is narrow, so you will be crossing over the line in places. If you're comfortable driving in the mountains and not in a hurry, it is a beautiful drive.
A much easier drive of mostly freeways and only about 50 miles longer is:
I-90 west to Ritzville, WA
Hwy 395 (turns into I82) south to
I-84 east to Palisades Corner, ID where you will get back on Hwy 95 south
On edit: If you decide to take the second route I posted, then I would take Hwy 2 out of Sandpoint and pickup I-90 in Spokane.
Bob, Sherron & Kinsey (Goldendoodle)
2009 Tiffin Phaeton 40QSH
2014 Jeep Cherokee Limited