Given that the future of programming is functional...
Since when did we agree that it is?
Look, no less than Anders Hejlsberg has noted a movement towards a functional style of programming, specifically in C#, but I highly doubt that even he would categorically state that 'The Future of Programming is Functional.'
at some point in the nearish future I want to be paid to code in a functional language, preferably Haskell.
Assuming I have a firm grasp of the language, plus all the basic programmer attributes (good communication skills/sense of humour/hygiene etc), what should I concentrate on learning to maximize my chances? Are there any particularly sought after libraries I should know?
First, you need to fully appreciate the tradeoffs between functional and imperative programming. Once you do, you'll be able to identify problem spaces in which functional programming can facilitate a vastly superior solution, relative to imperative programming.
All things being equal, I think a familiarity with advanced computer science topics, a graduate C.S. degree, or both would help you towards this goal. [Emphasis: Formal, classroom education is not a requirement. It's just that some classroom discussion might further your appreciation and imagination in this realm.]
Alternatively, would another language be a better bet, say F#?
Don't worry so much about which language you choose.
Choose the one that you like best, and then develop your appreciation for the functional paradigm. The syntax of the other languages should be easy enough to pick up afterwards.
(I'm not too fussed about the kind of programming work, so long as it's reasonably interesting and reasonably well paid, and with nice people)
Good - That's the way you should be.