re 1) one of the primary limitations of the lambda calculus wrt concurrency is that it does not model time--there is no way to determine how long a computation takes. An example of a function the lambda calculus cannot define is f(x, y) where the fastest computation of x and y wins. You'll see that function pop up in a number of places in the Haskell world, where it is called "amb". This function is obviously important from a pragmatic POV but it turns out it is also important when doing formal work as well: see the parallel-or/full abstraction problem for PCF[0].

My personal favorite concurrency formalism is the Chemical Abstract Machine[1]. The y-calculus is a neat extension that preserves the spirit of the lambda calculus, but also permits (purely non-deterministic) concurrency.

[0]: http://en.wikipedia.org/wiki/Fully_abstract#Abstraction

[1]: http://www.lix.polytechnique.fr/~fvalenci/papers/cham.pdf