Hope you enjoy your stay in ND! Sounds like you've got a good plan. I'm rather new to ND and so am exploring as well. I don't know if you'll check this while traveling but I thought I'd add my two cents.
I don't know if you're taking back roads or not, but on your way from Bismarck to Devil's Lake you may want to stop in Medina for food--I've heard the Firehouse Rib joint is good although never eaten there myself. Also, someone told me the cafe there serves some local German dishes which are also good. From Medina, you can venture north to Chase Lake National Wildlife Refuge and hopefully there see some nesting American White Pelicans. Potholes around Chase lake are also great for birding/nature. In Devil's Lake, I enjoyed a drive and short hikes through Sully's Hill Wildlife Refuge (elk, bison, prairie dogs).
I personally enjoyed the North Unit of TR and there was a great restaraunt in Watford City if I remember correctly.
Medora area has lots of petrified wood and south of the park is forest service land (or is it blm?) if you want to do some more exploring.
A drive down the Enchanted Highway is silly fun if you have time.
Bismarck is a fun town although I haven't explored it enough. I think JACombs gave some good suggestions.
I would suggest a stop in Jamestown at least along your way from Bismarck to Fargo. There are now 3 white buffalo here and the National Buffalo museum is a nice quick stop. Of course the World's Largest Buffalo is a must-see!
Valley City is also a quaint little town and the scenic byway along the Sheyenne River is really nice this time of year. I guess the Pierre Shale in the VC area does contain some fossils but I have not come across any road cuts that contain any myself.
I second the visit to the Hjemkomst Center in Moorhead. Not only is there a viking ship, but a gorgeous hand carved wooden church.
For more ND geology (the book you have is good I agree!), you may be interested in receiving the NDGS newsletter or reviewing old ones on their website if you haven't already.
Looking forward to your review, especially any special geological features you may find!