The olmec people

constructed giant stone monuments.

built pyramids out of blocks of stone.

developed a writing system with pictographs.

created a system of numbers that included zero

constructed giant stone monuments.
- I think this would be the correct they built Colossal Heads  around twice twice the size of people.

built pyramids out of blocks of stone.
- no, their pyramids were rather made of clay.

developed a writing system with pictographs.- yes, they did. But the Mayas developed it further to a full script- yet, the Olmecs did have a photographic script

created a system of numbers that included zero - we can find 0s in their writing system, so yes!