Most of the guidebooks for WA (the best known of which are published by the Mountaineers) are day-hiking books. Much of the Mountaineers books have been incorporated into the trail descriptions on the Washington Trails Association website, www.wta.org.
The one caveat on the Spider Gap to Lyman Lakes route is the long snowfield you need to descend. It's a good idea to wait until the snow is mushy, say mid-afternoon. On a cold morning, an ice axe would be needed. I had no problems at all using a single hiking stick on a fairly warm afternoon. EDIT, later: I didn't try to glissade; I plunge-stepped down.
Most of the Devil's Dome loop is in national forest land (Pasayten Wilderness). It's only the section along Ross Lake (East Bank Trail) that requires camping permits, and that will be crowded because of the boat traffic. Ross Lake is actually in the National Recreation Area rather than the N. Cascades NP, but the same rules apply as in the NP except that hunting, dogs and power boats are allowed.
Note that out here in the Northwest, most USFS trailheads require a parking permit, called the NW Forest Pass. It's $5/day or $30/year, and is to be hung from your rearview mirror while your vehicle is parked. You'll have to check to see if it's required at the specific trailhead you'll be using.