In the last 3 tournaments I played Necros quite successful with following setup:
2 WW
2 Ghouls
2 Wights
6 Zombies
5 FF or 4 FF and 1 AC for KickOff events
3 RR
Maybe you can drop the FF to 2 for another zombie, but 12 players should fit.
Don't forget that you can raise a dead, if you manage to kill an opposing player. Flesh Golems aren't worth their price, but it depends on how you play the Necros.
I usually let my WW score in offense and handle them like blitzers behind my first line of zombies in defense..So it all depends on your playing style, but never ever leave the WW in blocking or blitzing range. Try to avoid that your opponent can blitz/block him or you will have him surrounded by other players and the foul always comes next..120 gp lost in that way really hurts

Use your wights, they come with block and have a decent 6 movement, so you can use them as blitzers too.I usually give tackle to them to get rid of those blodgers, but also a WW with Block and frenzy is often a good choice to push some players into the fans.Sometimes people tend to forget that and prefer to run at the sidelines

I really prefer the handoff game, where my ghouls pick up the ball and hand it over to another WW, with the catch skill more reliable than the other way round..Worst case is when you're unable to pick up the ball, so ever leave a zombie and another ghoul to put tz around the ball in case you didn't manage to pick up that bloody thing..
Cas?? +2 on armour roll is a nice thing to have, so you're able to outman even the high av teams like dwarves or orcs..
Also regen is a nice thing, as it really helps to stay on the pitch with more players than your opponent, thus leaving you in a better situation to control the game...
cheers,
Utak