Here are some ways to say "It all begins with an idea":

• The idea is the starting point.

• The idea is the seed.

• The idea is the spark.

• The idea is the foundation.

• The idea is the genesis.

• The idea is the conception.

• The idea is the brainchild.

• The idea is the inspiration.

• The idea is the catalyst.

• The idea is the driving force.

• The idea is the impetus.

• The idea is the motivation.