Yes, if you work in a professional context, you can—and must—purchase a professional license, which is designed for businesses, associations, and organizations. However, if you are a private individual, the Personal license is the right choice for you. If you'd like additional features or wish to support OCCT further, you can opt for the Personal + Patreon or Personal + Steam editions, available for a monthly fee or a one-time purchase.
Just one. OCCT's licensing model is straightforward: Personal users need one license per household and Pro/Enterprise users need one license for their whole company. There is no limit on the number of concurrent instances or the number of computers you can test. As long as your license is valid, you're all set. Please note though that sharing or redistributing your license outside of your household or company is strictly prohibited.