At least 3 Stocks. The typical rules for Melee / PM is 8 Minutes, 4 Stocks each. That's 2 minutes per life - and I can definitely get 1 kill in a 2 minute timed match in the demo. I say three, however, because A) they are somewhat longer than previously, B) Have to take Respawn Time into account, C) Some people definitely stall more than I do, and D) I'm not all that fond of 8 Minute Matches.
Also, as far as custom moves go, I think they should be supported, but there should be an "official" list (Back Room) of banned custom moves - I have a feeling some of them will be unbalanced. This also gives chances to rebalance top-tier characters, because you can help to balance out their moveset by replacing their base specials with one that may be less effective. Just imagine if we had this mechanic for Brawl - you could rebalance Meta Knight by switching out his specials for less-OP choices.
Also, Battlefield is more than / as balanced as Final Destination. Just think of it this way - Mew2King says that if FD was the only stage in Melee, Marth would be the best character. That would be fine by me - but I'm not sure how the Fox fans would react to that. I also really like PM's Pokemon Stadium 2 - its boring, yes, but its possibly the most balanced stage yet.
One last thing - Nintendo, why did you not give us the option to turn off stage hazards? Get rid of Yellow Devil on Wily Castle, and that stage could easily be one of the best in the game. Even as much as New Character / Stage DLC, I'd like to see DLC for more options (more detailed custom controls, item frequency, Online Smash Run, etc).