Unless you have very cheap players then many teams only start with 11 and an Apo if you can afford it.
As well as the cost also consider how fragile your players are. If you are playing as skaven with their AV7 on most players you'll need more than 11 players. If you are playing as orcs with mostly AV9 you can probably get away with 11.
Unfortunately there are so few models available at the moment you're very limited regarding how many players and which positionals you can take.