What a project to take on! What hymnal are you doing?
To remember the first line, I think you just need a picture that reminds you of that line. I wouldn’t try to come up with an image that corresponds to every jot and tittle in the line; just an image that makes you say, “Oh yeah, that’s it!”
I don’t think it’s necessary to remember the number of verses until you start memorizing the hymn. Though, to separate out verses, I have started by creating X number of journeys that begin with the central image for the hymn, going in X number of directions. That helps me keep them straight. However, number of verses is far less important than getting the hymns down.
If you find that there are a lot of similar lines and verses (which is a problem with me and my study of ancient Hebrew right now for the project I’m doing), I offer a suggestion: make the image different every time. For example, if there is the word “city,” don’t use the same image of a city over and over, but use a different one. Perhaps one is a small city, another a large city, one is an ancient city with walls, another with a lot of roads, one has few skyscrapers, one has many, one with much traffic, one with little, etc. I’m doing Hebrew memorization, but I can only use the words melek and nathan and yashav in so many sentences before they all bleed into one another.
But then again, the memory champs here for numbers and cards are using the same images over and over and over all the time. Perhaps they have a different opinion, or insight they can offer?