You've read my mind sir at making this as I myself wanted to make this but I have alternative ideas from what you presented.
First off the ranks of which the gauntlets should go like this (from lowest at top and strongest at bot);
Cactus spike leather gauntlet (does less damage than stone but lasts longer)
Stone spike (breaks easier due to being just stone, also not cobblestone. Smooth stone)
Iron spikes (reliable, can have poisons set on them)
Diamond spikes (can be enchanted but no poison otherwise its to OP)
Obsidian spikes maybe?
Second off none of these should be indestructible, that's ridiculous. Even swords and diamonds themselves can break. Also none should be an instant kill, maybe the diamond or obsidian could be a 2 hit but still, it should have its limits
Third, you did get the spike idea right about making them in a triangle for one spike, but to make the gauntlet the top row should be spikes, and the rest should be leather or the middle square a gold nugget or red stone powder for extra power and looks. Oh the red stone can illuminate the surroundings a small bit so you don't have both fists raised in the darkness.
Fourth, I liked your ideas for the coal gauntlet and gold ones that can hoe but these should be for fighting and although those would be handy to have, its just not very good or necessary to have.
Fifth, They gauntlets should not work as an inventory item. They should either leave a space on bottom inventory space for using gauntlets with nothing in hands or have extra boxes on far sides for dual wielding the gauntlets.
Sixth I do like the flint idea but it should not just light everything forever only the mobs. I say it should be used with the iron or obsidian gauntlets as an added bonus, but to make it you would do all the same but on top 2 spikes on sides and 1 flint in middle the rest being leather except for the exact middle piece being gold nugget or obsidian.
In my minecraft games I don't use swords, I just don't They're big, clanky and I like my fists much better. I would like to help you as much as I can on this mod but I am not an expert at making mods or anything like that.