Since this is for a comic book, you'll be doing a lot of postwork anyway. Why not render the crowd piece by piece, then put it all together in Photoshop? Even low poly figures will choke your machine if you have "hundreds" of them.

Since this is for a still image, and not an animation, I would render the crowd in many different pieces, then layer them in Photoshop. That would have the advantage of allowing you to adjust the position, scale, etc. without having to re-render all week.