By your first answer, I will assume you prefer a Spyder which maintains an authentic appearance (wide five lug wheels-no chrome, correct lamps, windscreen, oil cooler grill, fuel filler, interior, etc.). Like Larry said, get the Ludvigsen book and compare the photos to the replicas. One other noticeable diference that I have learned to ignore (thus far) is the subtle difference in the rear fenders. The replicas are a bit higher and more pronounced. Though I have seen other replicas with even more exaggerated features, this is mostly noticeable to those of us who have studied the photos over the years or have had the great fortune to see an authentic Spyder.
Also, check out this site for great photo references: http://users.tellurian.net/robert/spyder/index.htm
Basic mechanical skills should be enough, assuming you have a mechanic in mind to handle the more advanced needs. An old-school mechanic with VW/Porsche skills is ideal. But one who knows his way around a carbureted engine may do in a pinch. Someone who works on replica/custom/hotrod may also work well.