Boris make some good points there. I don't agree that we should be restricted to his 24" rule; that's obviously personal for him.
I think having a pretty clear idea of the effect desired will help make options for construction clearer and experience helps, too! Lead's visual advantage is perfectly parallel edges... consistency. This is helpful in geometric designs, for example.
I suggest trying a very simple 6" square with an apple, leaf and four or five background pieces. Draw the organic, tapering, wiggly lines as you wish. Use lead... a small size or two or three, I'd think. Now, try to see how you might taper some leads to enhance the leaf point or make a leaf edge or stem more sinuous than is practical to cut in glass. Try it. See how it goes.
One method I've used in planning my leading scheme is to actually draw the intersections full size on the cartoon. For easiest visualization of the glass pieces, I may draw lead lines (cut lines) in the traditional way with two lines, one for each side of the heart. "Little railroad tracks" said some early observer.
Then, I add the edges (sight lines) of the intended leads. This helps me to see how lead joints can be planned for the easiest construction and desired result. I do all this in pencil so I can make as many changes as needed.