I did the Trans America as a first tour. I was joined by my daughter and a friend who had only a few short training rides under their belts due to the busy schedule of finishing their senior year of college. I think their longest ride pre tour was 33 miles. We all did fine.
My advice is to keep it simple. I don't know what your budget is but you don't have to spend a bundle. We went with inexpensive bikes and gear and I really didn't want for anything "better". I like some of the less expensive options better, some as well as the top of the line stuff, and only a few where I would like to have had nicer stuff.
The tour will be pretty much the same experience whether you are on a $599 Windsor Tourist like ours, an LHT, or a $5999 high end bike. It really isn't about the bike. When I think back on my tours I really don't think about the bike much. It is much more about the people and places.
Stuff like racks and panniers...
I like my Blackburn EX-1 rear rack, Nashbar low rider front rack, and Nashbar waterproof panniers just fine and really see no need to upgrade them.
Tent, sleeping bag, and sleeping pad...
We were OK with inexpensive stuff like a less than $100 Eureka 4 man tent (for three of us), an $80 Slumberjack bag, and a regular Thermarest pad, but these items are ones where spending a bit more will reduce the load. I have since bought a lighter tent, sleeping bag, and a Thermarest NeoAir pad. That made a substantial reduction in the load and increased comfort.
My advice is to be skeptical of spending more for heavier items. I am inclined to splurge only if an item is at least as functional and lighter. Avoid stuff that is both heavy and expensive.
Some experience with some kind of self supported camping is a huge plus and is probably as important as tons of miles of training. At the very least know how to use all of your gear.
Training is a plus, but on a coast to coast tour you can always start out taking it easy and ride yourself into shape. Just don't over do to soon.
Remember, a tour is about touring not about having stuff. The gear is just a means to an end.