Yes, depending the the context of the verb tense, it could be correct. 'By me', however, is simply not natural, so don't use it. We would use the active voice to convey personal confirmation. I am not sure of the context, so cannot comment on whether you should use 'has been' or whether you should use 'is'.

Yes, it is correct.

Yes, it is correct. Confirmed here is a participle that functions as an adjective. It can also be seen as a sentence in the passive voice with no mention of the doer of the action.