Less discussed aspects of solopreneurship

Few things I am seeking answers for.

1. What are the legal things I need to take care off before I launch my SaaS? Do i need a registered business before launching? At what point should I consider getting an attorney and accountant (if at all)?
2. Should I have to pay for a business email address before launching my product?
3. How does taxation work if revenue starts coming in?
4. Can I be in country X and launch my product worldwide without registering a company in each country?
5. Someone told me I need an export license to be able to provide a SaaS service globally. Is that true?

I feel like these are some topics that haven't received much attention in the SaaS communities that I have seen thus far. Would love to hear your insights, tips, and tricks. Thanks