I'm no expert but I think you can thin that herd quite substantially.
1 heavy commercial machine with walking foot for heavy canvas and leather-you probably won't use it much.
1 good old straight stitch machine. I prefer a dedicated straight stitch machine, I think they're a little quieter and smoother than most zigzag machines and they make a prettier stitch.
1 zigzag/decorative stitch free arm machine. I'm thinking like an old Elna, Viking or Pfaff with cams.
Realistically a free arm is good for mending, patching, things of that nature but most sewing can be accomplished with a flat bed machine.
A serger is optional. There are plenty of other ways to treat edges and seams so they don't unravel.
After you have 1 good running sewing machine the rest aren't really need based anymore.
Rodney