I assume that you mean that you will ride the Western Express to the TA since the TA does not go through Utah. If you go east from there you will be missing the best parts of the Trans America in my opinion. If possible for an east bound TA I would start in Oregon. Your call though.
No experience with the Jamis Auroras and Bianchi Volpes, but I was happy with my Windsor Touring ($599 including shipping) for the TA last summer. The most popular touring bike right now has to be the Surly LHT complete and it is under $1000 including shipping.
I have tried both and prefer panniers to a trailer. Some like the BOB trailer.
The Nashbar or Performance waterproof panniers are cheap, durable, often on sale, and we were well satisfied with them. We liked the Blackburn EX-1 rack on the rear and performance or nashbar clones of the Blackburn Lowrider on the front. All of that stuff is reasonably priced and it goes on sale often. Ours was all still like new after 73 days on the Trans America.
For cold weather riding pile top with a shell over it and a pair of winter weight tights (maybe windproof in the front) work well. Hands and feet are the hardest part of staying warm. Shoes loose enough to wear thick wool socks help. Tight shoes cut off circulation too much for cold weather riding. Some kind of booties over them help too. Down to 10F I am OK with some Cannondale long fingered gloves that I have. Sorry don't know the model.
You might find our journal of the Trans America interesting and useful. Also read other journals on cgoab.http://www.crazyguyonabike.com/doc/staehling2007