OH OH OH I get to be the one to tell him to look at the sub-$750 road bike thread!
Look at the sub-$750 road bike thread.
Check out
www.roadbikereview.com for reviews of the bikes you see in there. Shop around, make sure to get a good fitting bike. That's the most important thing.
I can't comment on back problems. I'm not even in my mid twenties...
Check out the clyde forum. There are plenty of big guys on bikes.
Can't comment on that model.
Saddles are very personal. If the one you end up with doesn't fit well, you can always get another. There's a huge difference between walmart saddles and road bike saddles, so what you describe may not even be a problem due to the different shapes.
*edit*
Lemond is a very reputable brand. Their bikes are actually made by trek. Their geometry is geared to people with a longer torso. Individual frame manufacturers have slightly different frame geometries. This is one of the reasons that fit is so important.