Lots of tips on this site.
You've obviously made a good start. Getting the atlas was a good move. Many of us travel with an atlas, AAA maps and State issued maps, which are available at all visitor centres. As well of course we have our electronics to help find specific addresses, when required.
To get many more tips, spend some time reading the Roadtrip Field Reports Forum. Those are the reports of people's actual experiences, rather than just suggestions. Many of us have multiple trips in that forum. By doing a search, you will find quite a few of solo trips.
With accommodation: be sure to inspect the room before committing. Besides cleanliness etc., be sure to check the smoke alarm is working (many a time I have found it to be disabled) and that the door has a lock which cannot be opened from the outside - such as the chain lock.
You might also like to check out these two pages - The solo trip - The art of the roadtrip.
Lifey
Be careful not to crowd that itinerary.
Mindy, as you can see from the responses so far, there is much to see between Chicago and Portland. Over the months, until your departure, there are bound to be more added. as well as the ones you find yourself. There will be points of interest along a northern route, and along the southern route.... and the many routes in between.
Don't be overwhelmed, but choose carefully which you will include, lest you should not leave yourself sufficient time to really enjoy each one. Sometimes less is more! This of course also leads to the comments above about not just crossing off States. There is so much to see everywhere, and you'll want some flexibility for those surprise spots along the way. Sometimes it takes several visits to see all you want to along any given route, or in any State.
For example, next year I hope to be driving to and through Alaska for the fourth time. Want to see it all just one more time, in case I never get back there.
Lifey
In case you did not see this....
Just came across this thread, and thought you might like it.... get some ideas from it.
Enjoy
Lifey