Yes it is legal IF "a principal party to the private conversation consents expressly or impliedly to that installation, use, or maintenance and the installation, use, or maintenance is reasonably necessary for the protection of the lawful interests of that principal party." You need to be the principal party protecting your lawful interests.
Relevant law in WA: SURVEILLANCE DEVICES ACT 1998 - SECT 5. Subclause 3(d)
Maybe. Depends on a few factors ( I don't know them all) and the judge of the trial. What you can do to get around the admissability of a verbal recording is to transcribe the conversation and attest it is a true and accurate record of the conversation.
I think the deciding factor would be if it is in a private or public place.
ie if you are screaming at some one in the street you may be recorded as you don't have an expectation of privacy.
If your in a lounge having a chat you would have an expectation of privacy.