It doesn't have to be 30, necessarily. But it's generally a good starting point- 35 max, 30 optimally. Any more, and your deck will most likely be too unwieldy/unreliable to be effective. You definitely have too many creatures- cut out at minimum 4 creatures, I suggest 6. Keep only what you need for 1 overall strategy for victory. You can splash in things that aren't necessarily related to your overall strategy, but you definitely need to focus on that first.