1:
WF is a big area; I'd start with a book, probably the Schmidt/Shukla -
but it is also a *foundation* not a product
2:
I asked something similar of Mike Taulty; his response is that by
necessity, there is, yes, additional processing on the code that is
transforming the expressions to LINQ, and data to entities. But this
is generally trivial compared to the network overhead of database
queries, and is on your scalable infrastructure (i.e. not the database
server). Add composability (which can actively reduce network IO,
rather than post-filtering after a big query). And of course the
development time, which is vastly more effective.
3:
Well, LINQ and WF are completely unrelated, so I doubt you'll find all
3 in one place if you want depth...
Marc
