If you need specific advice about tax liability or incorporation decisions, you may want to talk to an attorney.

Incorporating in Delaware does not necessarily make a corporation a Delaware resident only. If a corporation operates in California, it is probably subject to California taxes. In general, a corporation can be a resident of both the state of incorporation and the state of its principal place of business.

For sales/use tax, owning property in California or having regular employees in California may be enough.