Can someone please help me with these user research problems? [on hold]

I am teaching myself UX and there some aspects of it that I just cannot comprehend yet.

1. When working on a fictional personal project that will only serve as a portfolio piece (i.e. briefbox projects), how can I find the appropriate data to create user personas? I want to emphasize my process but I feel that the lack of data and no client or real users are a major road block.

2. Once you are working with a real client and you get at the research stage of the project, how does the access to the customer base usually work? In other words, let's say you start using a tool like Optimal Workshop to run a study. Do you send the link of the study to the client and they send it to their customers or does the client give you a list of e-mails and you send the link of the study directly?

3. If you start working on a new project for a new business that has no customers, how do you find the people to send your surveys, interviews etc. ?

Thank you very much for your time!