I've done something like this for my mod NT; if you're looking at stat boosts, then I'd recommend a heavy boost for Vit/Spr (30-50) to make it noticeable and maybe something a bit more sparing for Magic (I found that weapon + armour boosts together can make Magic a bit too strong if you're using +20, etc. so 5-15 seems more stable). I also went with a similar weapon power range; I went with 50 as the cap which shrunk the differences between each weapon.
For effects, you can use Elements & status ailments to give pieces a unique ability, but be wary of using Slow/Stop for armour defence; Time Magic statuses seem to be 'combined' in some weird way so defending against Slow will mean the character can't gain Haste either.
One thing to remember is that defensive stats aren't as weighted as Strength/Magic are, so differences in armour will need to be more pronounced. Problem with that is if the armour defensive values get too high + VIT/SPR bonuses on Weapons/Accessories, you can end up hitting the 255 cap too soon. I tried a build where Iron Armour had 1 slot and 70+ defence but it didn't make as dramatic a difference as you might expect.
Another thingie you can do is adjusting the damage formulas, targeting, etc. You can make weapons that hit everything on the field (including your team) for a 'blender' strategy, or make them deal %-based damage, damage/drain HP/MP, restore HP, ignore defence, etc. Just be wary of HP drain, it combos too well with Counter Attack Materia so maybe give it a low base power or give it Gravity element to keep it under control.
And finally, when editing flavour text for equipment keep in mind that there's a size limit for the kernel so keep it as compact as possible. Abbreviations for stats would be a good idea.
