This is less a California issue than a US remote business issue. Any number of states have labyrinthine regulations regarding who must file corporate income taxes, who owes state sales taxes, how you must acquire unemployment and disability insurance, etc.

And you're just getting started with the states. If you happen to employ someone in a bureaucratic or tax-ridden municipality (e.g. Philadelphia, Seattle, NYC, tons of others), then you are going to have processes to file fees and paperwork with obscure offices and locally sanctioned accountants (looking at your Pittsburgh) and insurance companies.