I'm not sure what constitutes medium sized when it comes to an armor mod. Are you looking for just a ton of different armor types? Do you want customization? Early game, late game, or both? Do you want it based off RF or EU? Is there a theme to your pack? Is it OK if the mod adds world gen? What other mod armors will it be competing against (so we can judge a relevant power/investment ratio).
You've given us a bit of info, but not much considering the number of mods out there.