Tyler, I've built several hundred of these little buggers - if you cut the bases down into rough ovals (diamonds, polyhedrons, whatever - just make 'em smaller) before you glue them to their stands you will find you have far more latitude when ranking them up.
My minis are fielded on 45x50mm bases, ranked 3x2. I don't use the loading poses because they are very static looking. For more disciplined units, like the Brits, I avoid the firing poses too unless I intend to make the whole unit firing. If you do want to mix in the firing poses, I suggest you group them together at one end with a 'spoiler' mixed in - warning, this tend to make them look like an undisciplined mob, but I thought this was appropriate for my Spanish units! Make sure you build shooters from poses with both feet on the ground!
I generally rank advancing poses, sergeants, and officers in the first rank and shouldered muskets in the second rank. If you drop in a casualty figure (something I do only rarely - don't want my whole army to look bloodied), you can add an advancing figure in the second rank as it looks like he's stepping up to fill the gap.
Hope that helps!