Bike Choice
The 7.5FX could work, but if buying a bike for the trip I would buy one designed for the task at hand. The 7.5FX has flat bars and I would recommend drop bars. It also doesn't really have low enough gearing, but that is true of some of the dedicated touring bikes. Most of them have an adequate cluster on the rear, but some have too high gearing on the front.
You can order a bike on line if you decide on one that isn't available locally. The Randonee, LHT and Windsor Touring can all be ordered. Several of the bikes mentioned are in the $599 to ~$1000 range. I used the Windsor Touring ($599 including shipping), but changed the crank (Sugino XD600, $80) to get better gearing.
All that said bike choice is really not a major factor on the the success of the trip as long as it:
- Has low enough gearing.
- Fits well and is comfortable.
- Is durable enough.
- Can carry your gear without problems.
Training
Nothing wrong with training and at a minimum you need to be used to spending all day in the saddle. Personally I don't train with a loaded bike and don't find it necessary. You can train as you go, but it is important that your butt is used to saddle time.
Daily Mileage
Lots of people find that they need more time than they think. I was in pretty good riding shape when we started and while the first week while my partners were getting in shape was slow for me, I did not find the daily mileage to be a cakewalk by any means.
We did cross the Continental Divide 9 times and went over many passes, but the climbs up the passes were not always the parts I remember as being hard. Days with 100+ heat and days with a strong headwind come to mind. We actually did better mileage on mountain days sometimes than days we expected to be easy.
Also remember that sometimes the towns will be 40-80 miles apart which means stopping where there is a town and limiting your choice of how many miles you do that day. Often you need to choose between 20 miles less than you want to do and 20 miles more.
Starting Point
Don't rule out hopping on a train and starting farther up the coast.
Riding Alone
That is a personal preference. Everyone is different and we met quite a few people who were very happy riding the TA alone. On the TA you will meet lots of other riders and can ride with someone if you choose.
GPS
I am a big GPS user. I use it sailing, hiking, kayaking, canoeing, and running. I started my TA with one and sent it home the first week. You really don't need it on an AC route and we didn't miss it when we were off route. Heart rate, cadence, etc. are
not what a coast to coast tour is about to me. In fact the bike and gear aren't either. The important things are the things you see and the people you meet. Better to just keep a journal and jot down the important stuff daily. That is my biggest regret, that I didn't write a journal until after the trip.