As to song struture. It has been noted that a popular song needs to have a beginning, middle, and end. It has been noted from time to time, that a song, popular type, should be about 2 1/2 to 3 1/2 minutes long.
A song too short may not be a song at all and one too long may get too repitious.
A song should not give away everything until it is ready in the song. In other words, a bit of mystery. But of course the song still has to have some contunity instead of a bunch of words just thrown together.
A song that is pretty long but works perfectly is EL PASO by Marty Robbins. Keep writing.