How many interview stages is too many

There's a job I really want - i tick every item on the job spec, but never known so many stages in the process before.

I've already had:

• Informal chat with the recruitment agency
• Walkthrough of my CV with the recruitment agency

The next steps are

• Formal interview with hiring manager

• Formal interview with a manager doing the same job for a sister company

• Formal interview with the CEO

This is for a middle management role paying ~£60k