Generally, the CEO or another founder will hack being both the head of product, and head of product marketing, at least until $1m-$2m in ARR, often longer.
You definitely need senior product experience as you scale beyond that, definitely by the $4m-$5m ARR range.
Because you need the help in Product and Product Marketing generally once things get complicated.
But … you need a VP of Demand Gen at $20k in MRR. That’s far, far, far earlier.
You need help in Demand Gen as soon as you have even a tiny stream of growing customers. And the hire should be almost immediately accretive.