Whatever works: I don't think I write lyrics the way you do, but if the English-composition approach helped me write, then I'd stick to it.
Once, recently, I got a "gift" lyric that came out of my head easily and quickly. On another occasion I had to work over the lyric for a long time.
If the song seems too short, you can (if so inclined) add an instrumental bridge passage.
If the song seems too long, but you can't bear to part with any of the verses, then consider devising a "short version" in which you leave a few verses out, and a "long version" with all of them in. Which version you sing would depend on your sense of your audience.
Keep in mind, though: I've probably written fewer lyrics than you have!