Where can I find an overview roadmap with milestones and date estimates?
The best place is to go to projects in the Celo GitHub repro. There you’ll find Betanet => Mainnet plans. Note that the team building Celo works in an agile way so boards tend to be quite dynamic.
Betanet - Dec 4th 2019 - The Great Celo Stake Off (announcement here)
Betanet + 1 - Audit readiness
Betanet +2 - Things that don’t need to be done for audit but needed for mainnet
Mainnet - Things that don’t need to be done until mainnet launch
Note: Betanet is called Baklava. See here why Celo’s networks are called food names.
Given launch is pending feature completeness and that all security audits passed the team is working against a checklist rather than dates. Current estimated mainnet launch (pending all goes well) is mid Feb to early March 2020.