Is saying "Io sono una ragazza." considered awkward for a native speaker? Or is it more formal, or is there really no difference between using "Io sono..." and just "Sono..."?
It depends. You can say "Io sono una ragazza" if you want to hightlight the fact that you and only you are a girl. For example: "Siete tutti ragazzi?" ("Are you all boys?") "No, io sono una ragazza" ("No, I am a girl.") Everybody will understand you if you want to add the pronoun in other circumstances, but we tend to simplify by not using it.
Sono = I am
una = a
ragazza = girl
essere = to be
io sono = i am
tu sei = you are
lui, lei è = he, she is
In English, the verb 'to be' changes a lot depending on the subject pronoun. In Italian, this is so normal for all verbs that often you don't even need to say the subject pronoun because the verb makes the subject obvious. io sono = sono
This page discusses subject pronouns. http://italian.about.com/library/fare/blfare113a.htm
This conjugates essere (focus on the present for now) http://www.wordreference.com/conj/ITverbs.aspx?v=essere
And what MissSpell said is also true for spanish and brazilian portuguese as well
Rolling the "r" in Italian doesn't come easy. Is it just a matter of practice, or what?