It looks like you've already been doing your homework! I've spent a number of short vacations in the area, and have some comments...
I've been to the Lost Coast for a long weekend once (staying in Shelter Cove), and frankly couldn't find much of interest there. IMHO, the Mendocino coast is much better, Big Sur is much better, and the southern Oregon coast is much better. I'd do the southern Oregon coast (Brookings area to Florence) instead, or Mendocino south of the area you're looking at. Still, I've only been to the Lost Coast once, so, if you've talked with others who've found more of interest there, then go for it.
For lodging, tripadvisor.com is your friend. There are Best Westerns scattered around the area; there's an especially nice one in Brookings right on the beach (BW Beachfront Inn), with sea views. I stayed at the one in Crescent City years ago - it was OK, but nothing special. (Crescent City is a working-class town, nothing for tourists except being near the redwoods parks.) In Eureka, there's the historic Carter House, in Victorian buildings, which could be fun - but the one time I stayed there it was noisy (thin walls). Still, being inside Eureka is nice, wandering around looking at the Victorian buildings is fun for a little while, and the restaurant options are pretty good. Or if you prefer, there's a very nice Holiday Inn Express (if you like simple but comfortable places) in the middle of nowhere along the highway near Arcata, just a little north of Eureka. If you want to splurge for a few nights, there's a great historic "grand old hotel" a bit south of Eureka called the Benbow Inn, with a great restaurant (fine dining, extensive wine list, etc.), where I've stayed several times - it's conveniently located for the Avenue of the Giants and Humboldt Redwoods State Park. I haven't stayed in Ferndale, Fortuna or Trinidad. Again, tripadvisor.com is you friend!
And staying part of the time at the north end of your range and part at the south end is highly recommended, to reduce time spent in the car.
Lisa