Does Wind Speaker blessing affect Olaf's W?

No. It's basically the same thing as his W.

Lifesteal does not seem to be affected by the mastery for whatever reason, probably better to take grasp of the undying on Olaf.

No it only applies to heals that you can give to others does not help yourself

but Olafs W increase all sources by a percentage per his missing health .. so windspeakers by description should increase that healing increase by 10%