After disabling displacements and shading to speed up navigation in the 3D view, placing the mannequin placeholders went pretty quickly. I wasn't sure how this idea would work, but it looks like it will be a real time-saver. Now I know how many models are needed and exactly where they will go. (Allowing for adjustments once they are replaced with real models, of course.)
As of now there are 26 unique models. Seems like a lot but I think it's doable. Counting duplicates and populations there will be more than 100 figures in the finished scene.