You can do any structure you want. I'm sure that some structures work better than others for ranking, but I doubt if many people outside Google really know in detail, and Google staff simply don't reveal details. For myself, I go by and large by the rule that anything that makes life better for my readers, will make my ranking better. That is what guys like Matt What'shisname always come back to and it seems to work for me.
The way I metaphorically see it, is each paragraph produces "Google love" and if they stick well together on a page, that page (keyword) will produce a lot of Google love. More good pages in a sub-directory/folder will make a "strong" and the sub-dirctories support the rootdirectory/homepage.
I'm sure "proper" seo experts will laugh this off as too simplistic, but it works for my site.
If you get the book I mentioned ( and read it ), you'll understand how to do it.
As for duplicate content: as long as you don't use the same text twice, there isn't much risk I think. Others may be more knowledgeable on this point.
It's a lot of work to do, but after you have mastered the basics of onpage seo, I think you should do all the writing instead of the B&B owners. You could add an interesting section to your website with people's reviews of places they have been and use that to add/alter your descriptions.
Another thing that is a must, is a blog. Both in terms of seo and as a point of interest for your users. If you can write blogs of half a page to a page at a time, put those on as often as you can produce them regularly i.e. if you can average 2 per week, write as many as you can, but put them on at evenly space intervals.
1. It's another thing that sets you apart from the rest.
2. It can create a group of regular readers amongst those that use different B&B's several times a year.
3. This is something that will spread over time and attract more readers and possibly mentioning of your site on other sites.