I've been 100% this mod every update for a while, and true story, I can never enjoy FFIV without it again. Considering that FFIV is quite possibly my favorite rpg of all time, I promise it is high praise and I am deeply grateful to 8bitfan and co!
That being said, a few suggestions... mainly regarding the post game content.
First and foremost, there are still commands and items that are too vague. Many abilities I had to test out in combat multiple times to find their use, and most ended up feeling useless by the time you get them. Edge's additional skills, Rydia's white magic, Dark Cecil's black magic, Cid's tools, and Kain's white magic all just kind of fall flat, particularly at the end game. Cecil's white magic very narrowly hovers above that point, but has more to do with his kit and melee attackers being fairly obsolete compared to their spell dumping brethren. He fits the position of off-tank very well, and that is largely to your credit!
On the flip side, Dark Cecil's skills are actually really fun in the early game, but by the end game... yikes. Bane will never catch up to throw or magic, and the cost to use it or Dark (which could really use some buffs) is extremely high. Yang, being the other physical front liner, also has a tough time. Kick is woefully underpowered, and his tankiness has the cap of 9999, meaning that by end game and post seed binging, he is going to fall right off the defense and offense ladder. He also suffers from a friend nearby, one Rosa the flipping all purpose monster, who can tank, hammer-murder, wash dishes, revive, heal, regen, and I guess she also has aim which would be a bit more fun if it also applied to her projectile weapon options (aim the chicken!). This problem doesn't even need to exist, really, since you're already so close to a perfect answer to his usefulness with brace! Just make him fully immune. So many of the extra game content bosses have scripted routines that can auto-kill a character or even majorly gib the party despite any other defenses. Having a full power Yang take a turn after that could be a whole new level of strategy.
Lastly, we have the children and the crybaby. I already knew going in that the option of another black or white mage would be amazing, and I was not disappointed. Their abilities still scale fairly decently, and actually give me hope of fixes for the less powerful options of their cohorts. Sure, twin hits a damage cap real quick, but until you get there, it is a moon-busting level up friend. Edward... oh boy. My first few times with this mod, I chucked battle items pretty often, but when I saw you added him to the end game, I knew better. What a monster. He is the anti-Yang, and that is not a bad thing. My only small complaint is that the last harp is quickly outshined by so many other weapons next to it, and he needs something to sing with... my only large complaint is that for a glitched character who doesn't level-scale... his health total is pathetic. I'm unsure if you were making him Onion Knight-esque, but post seeds he is bar none the strongest beast you can party with and very unique.
-Buff physical attack skills (kick, dark, bane) with something like a stat debuff that will actually reliably go off on enemies. In the case of Cecil, perhaps less hp drain and tack on an additional magic drain to compensate.
-Dig a little deeper into the magic tree for DK Black/Dragoon White/Caller White magic, and give Edge his goodie bag a little sooner. The tower linkage could help with this, I wager.
-Improve Yang's Brace to be immune to damage altogether for a turn. Tank a crush or a supernova like a true boss monk!
-More item descriptions? Clearly tier the items in damage scale maybe?
-Cid's tools are almost amazing, but if need be, give the poor guy some mp and buff them to being useable.
-Aim projectiles, not just bows. Instead of sing, perhaps "perform" to spam whatever debuffs are on any weapon? Slaying tail dance!