Copyright exists by virtue of creating the original work, BUT........registering with the Copyright Office is essential to avoid the he said/she said scenario over who really wrote the song. Personally, I wouldn't allow a label to release anything without a contract in place. Tell the label you want one. I think you're headed for some trouble myself. Go here to register your songs ASAP. You can register multiple songs on one form by having a title for the collective work (album title). Register them as both Performing Arts and Sound Recording.

http://www.copyright.gov/register/

In addition to copyrighting the songs, you probably want to either set up a publishing company or sign with a publisher and either BMI or ASCAP. You don't say what you mean by the label "putting out a few of your songs." If they are having someone else cover them, they have a right to do that, but have to pay you for the "mechanical rights."

At any rate, you have a good bit of homework to do. I recommend Passman's book as a good place to start, but there may be books more specifically directed at your situation.

I'm at the beginning stages of a similar situation... submitting songs to labels for artists to cover and release (hopefully).

Regarding setting up your own publishing company - Is this really necessary for a writer with no publisher? As a BMI writer, can't I simply collect the full 200% royalties without having my own publishing company?

As I understand it, there is a fee for registering as a BMI publisher and I'd like to avoid this if possible - But first and foremost, I want to keep 200% royalties.