IANAL, normally it's better to delay incorporation as long as possible, until you have either significant sales, outside investment, or some large spending (i.e. on patents, contractors, large cloud bills, etc.)

But since you already have a cofounder, it's better to incorporate as a DE C-Corp right away. And of-course hire a startup lawyer to set up all the standard protections in place, i.e. cliff, vesting, etc.

Also you will quickly see how serious your cofounder is.