Answer to your questions:
Q: Is the reference document mentioned is good enough for this upgrade?
A: Yes. High-level steps
Q: I am using SDL Web 8.5 and trying DXA 2.2.9 which uses GraphQL as providers?
A: There is no PCA Graphql feature in 8.5, It's available only from sites 9.0+ versions, you need to update your unity.config to use CIL Defaultproviders ...