James -
I read some of your earlier to get an idea about your experience.
Looks like you have done a good deal of riding in the Pac NW and camping.
I figure that you must be at least 30+.
About finding companions for a cross-country tour - -
My experience over 30 years has been that many say they want to, but few follow through.
Applies to both people online and esp. friends.
It takes a lot - preparation, saving, getting time off.
Not to mention similar interests in routes, motel/camping, style of riding, etc., etc.
Both the TA and NT are 4200+ miles - that's 10 1/2 weeks at 400 mi per week.
Will people have that much time? Need more time? Can they do 400 miles per?
For most of us, 400 miles in a week is no big deal, but for newbies it seems huge.
I've ridden cross-country a bunch of times - including my most recent last year.
Hadn't ridden back east for a long time - and I realize why, yet again.
Camping is hard to find and pretty darn expensive the further east you go.
So I'll stick with the western half of the US of A for now.
TransAm, Northern Tier, or something else?
You mentioned that you've done the Oregon and Wash parts of the TA and NT.
The NT really has a killer start for inexperienced cyclists with 6 passes in the first week.
Also, it can be pretty chilly - even rain/snow - early in the season.
Of course, the ride over Going to the Sun in Glacier NP is simply the finest out there.
Then there is twenty zillion miles of Great Plains - maybe thirty zillion.
The TA's route across Oregon is quite nice - some moderate climbs, but you have time to acclimate.
It's probably the most bike-friendly section of the most bike-friendly route in a bike-friendly state.
The TA over Lolo Pass is also sweet and drops you into Missoula - the Berkeley of the Rockies.
And few people have grumbled about the TA thru Wyoming or the Colorado mountains.
But then - - you get eastern Colo, Kansas, and all the dogs of Missouri and Kentucky.
(There's also the Lewis & Clark route from Astoria thru Missoula to eastern Montana.)
<<<>>>>
But, given your level of experience, why not craft your own route?
Do you want to start at ocean's edge or are places like Anacortes and Yorktown o.k.?
How much effort is needed to get to/from endpoints? Westport, WA is a great place, but hard to get to.
I might suggest a combination of the TA and NT - starting with the TA and ending with the NT.
That would require some kind of connector through the Great Plains.
Most likely Nebraska/Iowa. ANd it is hard to go wrong anywhere in Nebraska.
Most little towns in Nebraska have free camping and back roads have light traffic.
Plus the Sandhills are wa-a-ay more scenic than Kansas or North Dakota.
You could take the TA all the way to Walden, CO - then head east thru the Cache la Poudre Canyon.
Or you could cut east on US 20 from Dubois, WY across northern Nebraska - very nice riding.
(You could have caught the eclipse yesterday on this route, but I guess you saw it in Boise.)
Anyhoo - - thems is some ideas.