I just have a quick question. I'm thinking about starting a KitPvP server. I wanted to add ranks into the mix but I just had one question. Is it against the Minecraft EULA to add a bonus kit that comes with the rank? It wouldn't be like everyone else has leather armor and the rank owner has full enchanted diamond armor, more like everyone has enchanted iron armor and the rank owner has full enchanted iron armor minus a helmet or chestplate or something that isn't enchanted but is diamond. Or something fun to mess around with, like a knockback I stick or something. Nothing OP is what I'm trying to say. Would it still be against the EULA?
These bonus kits cannot change any gameplay aspect at all so the example you have given would be against the EULA. If you made different armor sets but they have the same protection values as the non rank kits that shouldn't be a problem.
The degree in which something is effecting gameplay doesn't matter if it does it isn't allowed.