The levels are based on the scope of influence and ownership: How much the organization can depend on somebody to deliver?
Levels are cumulative. Each subsequent level encompasses those preceding it. The higher your level, the more the organization (/can) depends on you to solve problems.
We are not fans of titles at MUI. We only mention them in the spreadsheet to give a comparison point with the rest of the industry. What matters a lot more than titles is a clear description of the role of each team member.
Your level is kept private. It's meant as a guide so you know what to optimize for.
The descriptions are meant as general guidelines, rather than an actual checklist. People should avoid any artificial attempts to accelerate promotion by checking off the items listed.
Product management levels
No. It's all based on how much risk you manage and your impact (leverage) on the organization.
Yes, we want you to be happy and sometimes you have to try something to know it's not what you wanted.
Your manager and your manager's manager.
It's up to you. There's no min or max time period for any of the steps in the career path. Every career is about self-development, if you've mastered your career path and are displaying traits of the next step then it's time.