not too long - last time I went couple of years ago it wouldn't take my uk debit card in their ticket machines - dont know if this is still the case. Take plenty of small change euros to avoid the queue at the ticket office!
how long it takes depends on which part of the terminal your flight arrives - it's a bit of a hike from 2a or 2b, and if your flight uses 2g you'll need to take the bus.
if you're heading for the RER to paris, a single ticket will cost you EUR8,50.