It's Idaho. Those are old mine roads, aren't they? I've only looped back on the highway or obscure surface roads.
If you're carrying your full kit on the bike for the return ride you want the sturdiest tire you feel like pushing.
There is a bike shop in Kellogg and, I believe, one in Wallace. Give them a call. There is a website for the trail and I believe the site either has a discussion forum or a contact listing for additional information on planning a successful road or mountain bike trip.
I've ridden the whole trail both directions. It's an amazing resource. Lots to see and do along the trail. Be sure to allow some additional time on your trip to visit the local museums and do the tourist stuff. And, depending on where you're coming from, there is so much in Idaho to see! Bring your fly rod and stay a bit. Spend some money.