It depends on the opponent. A rush deck doesn't need more than its midrange attackers. that is 2 x 6 =12. 11 or 12 pillars will usually do also. Total = 23 to 24.
That means you have room for 6 or 7 auxiliary cards that might improve on a sheer rush. You probably know a rush that runs into permafrost or phase shield is a bust, so there you can add some deflags, maybe some CC.
The other way to slice it is to play with 15 pillars and 15 creatures, some of them more expensive. I think this is dumb, because it will never be a rush if you draw the expensive creatures early. They just sit there in your hand.
There is even a rush possible with low level attackers, that is with about 12 pillars and 18 attack! This works well enough, for example for death. Problem is most elements don't have that low level attacker.