Two sets of eyes is ideal.

Making use of things like GitHub CODEOWNERS files can be very useful too, allowing for certain directories to require reviews from certain individuals or user groups. For example, a directory containing the Helm Chart for a service might require a review from someone in the infrastructure team.

Keep the entire team as optional but most reviews can be done by 1 or max 2 people.

0. I commit and push directly to master.

It depends.

0-2.

More than 2 is unnecessary.