optimal number of hands
At the point that the count dictates a max bet, spread to two hands with a bet of 73% of your max bet on each hand, with one or two other players. For three or more other players, spread to three hands with a bet of 57% of your max bet on each hand. This allows you to get more money on the table at high counts, reduces variance, and gives you a better chance of catching the good cards.
Of course this going back and forth from one to many hands is going to piss off the other players and will bring increased heat from the pit. One tip-off to the pit that you are counting is always spreading to multiple hands in high counts. You have to weigh player and pit reaction to the marginal gain achieved by spreading to multiple hands.
You might try reducing your minimum bet, and always playing two hands with other players at the table. This might allow you to actually achieve a higher overall greater spread in the high counts without the pit taking great notice. Also, dropping to just one hand in the really bad counts, giving you a lower minimum bet.
Good discussion of this in Chapter 2 of Don Schlesinger's book "Blackjack Attack". I suggest you get it if you are serious about the game. The entire book basically answers the question "How much should I bet and how much can I win?"