Those smaller 14 in rims probably will not fit around your brake system, as the 16's are the factory rim size. And like another respondent said, the smaller will alter the correct speed reading on your speedometer.
Maby you should just drive slower over rough roads.
You probably need to remove the carpeting and side mats in the trunk before you can access the fasteners for the tail light housings. Most sedans that I have had (GM and Ford both) have the tail light fasteners hidden my that stuff.
I know both the Haynes and Chilton repair book series have specialized books on bodywork and paint, and both cover the same topics. Your local library should also have something in the auto repair section of the card catalog.
With that low of mileage, you won't find a cheap one. Expect to pay over $10,000.
That being said, try autotrader.com, your local classified adds in the paper, or the used lot of your local Ford dealer.