I echo the views regarding touring bikes versus "normal" road bikes.
But for your 350lb friend I would suggest a better bike to start on would be a used rigid mountain bike, something like the 1990's Trek 800 series:
Several reasons:
- These bikes have low frames with heaps of standover room. If balance is an issue, I couldn't think of a more important design factor to build up confidence.
- They have sturdy 26" wheels which are going to be stronger than a 700C.
- The 1990's era mtbs generally didn't have suspension. It's one less thing to worry about. Most Clydes would, I guess, lock out the suspension anyway, and I would assume an uber Clyde certainly would. A lot of suspension bikes don't even have lock-outs.
- The low gearing on these bikes really helps somebody who is unfit and or overweight keep up momentum when the geography gets a bit hilly.
- Put some slicks on these bikes, and they ride just fine on the road,
- You stand a pretty good chance of getting a 100% chrome-moly frame. I could be 100% wrong, but is just seems to me that a 350lb guy is going to be better off on a steel frame than an aluminium one, and
- They can be obtained cheaply. So if it doesn't work out for you friend, he hasn't lost much. If it does work out, and he decides to upgrade to a touring bike or whatever, he hasn't over-capitalized his starter bike.
I have a 1997 Diamondback Wildwood mountain bike, stock except for slicks, riser handlebars and bar ends. It got me hooked on cycling and I couldn't think of a better entry level bike for a Clyde. I've moved on from this for most of my riding, but I still keep it as a backup bike and for riding with the kids.