I say 1000, some people will say lower.. but I don't think you get a good feel for the rules or missions at lower point values.
Plus if you have played other miniature games the rules will come to you a lot easier.
Dark Angels 1750 win/loss Record
Win - 23 (Belial helped wreck Ryan's puny Eldar)
Loss - 13 (Brice's Necrons wiped me)
Draw - 2 (The 13th hold out in alpha take and hold)