This (if this is really your first piece) is very good. The harmony you use is used too often, this is ofcourse not your fault

And as you are a starter to composition its ok to use them. They used by so many commerciall compositions, songs and so on. More interesting is how you structure your piece and modulate between the parts, how your textures how your theme is and such things. I can say they are all ok and from now an the work beginns for you. I hear that you have the ear and feel for harmonies and all that stuff. Now you should experiment, make many many pieces.
To become a composer is a relative thing and depends on what you mean with it. A composer for video games, a filmcomposer, a classic composer, a pop composer for a band, a comercial composer for commercials for example, or blues, or jazz or ... (there are so many kinds of composers).... For film and classical, you need the most talent and most knowledge (and much luck too) i think but for all others you need more luck then talent or knowledge.
Esim