Thanks all for helping me to think this through. There seems to be a difference of opinion about 9W. The better part of valor seems to make sense, so I think I'll take the scenic route, at least until I see the lay of the land myself. I'm OK with the distance, I've done more than 16 miles in the city without much trouble. I think it's mostly inexperience and unfamiliarity, and hills, that give me pause. I found that by extending the ride a mile, I can cut off some of the hills so the part in the middle is mostly flat. New route here:

http://ridewithgps.com/routes/1957089

That seems to be the thing to do? Also, the big hill is at the end going down to the river, so it might make sense to just take the plunge and take the route to the monastery, and decide if I want to tackle the big hill on the way back. Noglider, I want to get there before dark, so if I time the train right, I can give myself all afternoon.

Puckett, I appreciate the local insight. Have you biked these back roads, or 9W? Do you see any problems with the route in the link above? In Street View, the shoulders look narrow and crumbling, but then those pictures look old; there's no sign of the Rail Trail.

I've also prepared myself with a tube, tire levers, and patch kit (still have to get a wrench), and I'll practice fixing a flat, which I haven't done since high school. I've been meaning to learn, but haven't had to; I've had no flats, and there's always alternative transportation in the city (except in the aftermath of Sandy, but then the bike got me around powerless, trainless lower Manhattan better than any of the alternatives). Not so much in Ulster County. Anything else I should prepare myself with?

When it's all done, I'll probably think I overthought the whole thing. I overthought everything when I started riding in the city. So I ramble. Anyway, thanks all.

Here's hoping for good weather...