I know when saving a textarea you can use the nl2br() or str_replace to change the /n to br tags etc. However what im not sure about how to insert line breaks into a textare
Don't do nl2br when you save it to the database. Do nl2br when you're displaying the text in HTML. I can strongly recommend to not store any HTML formatting in the database (unless you're using a rich HTML editor as well, in which case it would be silly not to).
A newline \n will just become a newline in the textarea.