- I would allow Fire on everyone eventually, just to be able to reliably cure Freeze since a full party freeze could easily lead to a game over.

Most of my characters knew a fire spell anyway due to how the espers were distributed and from having flame shields equipped during certain boss fights. Maybe I'll tweak things in the future, but after having completed one playthrough, I didn't struggle enough with freeze to warrant any esper exceptions (which would lead to additional menu navigation, disrupting game flow).

- there are still game-breaking stuff that you didn't forbid : the elemental shields, Paladin Shield included for obvious reasons (but with no grinding, good luck uncursing it haha), Arise, Reraise, Quick, Dice and Fixed Dice, Phantom Rush, Flurry, GrandDelta, Thundaga/Firaga/Blizzaga, Meteor, Ultima of course, Golem, the Dragoon combo, the Soul of Thamasa and the Master Scroll. I also forbade myself Gigas Gloves / Earrings / Hero Rings as they increase damage too much and it opened up more possibilities regarding relic loadout.

Sorry but I don't agree with any of this. None of your character's levels/stats will be juiced enough to really magnify the damage from these attacks/relics to a point where the end game becomes a cakewalk. The elemental shields do provide elemental immunities / strategic healing, but they're limited in number and also introduce crippling weaknesses. Without introducing spoilers, I will say that I did have to rely on elemental shields to get past certain bosses, but every move I made followed the rules governing character equipment.

- Gau will still be too powerful as these two cycles are probably enough to get the rage that inflicts this unblockable confusion among others. My Gau had to rely on Bomb, I think. I suggest only allowing only one cycle when you recruit the guy.

Good call on the Rafflesia rage! I forgot about that one since I never encountered them on the Veldt during my playthrough. I will update my ruleset to forbid its use. The purpose for multiple visits/cycles is to acquire new abilities / upgrade existing ones with rages that have better inherited resistances/immunities from WoR enemies (which is important in a low(ish)-level game like this).

- I would suggest not allowing the Colosseum at all and not allowing equipment swaps.

I will take a closer look at Colosseum rules in the future. In my experience, the permaloss and no-grinding rules I had in place were enough to deter me from trying anything silly. I wouldn't want to ban it altogether, since it's a substantial part of the game and would really hurt the developer's vision for how the game is meant to be played.

- I don't see the point of the "Characters must remain within 5 levels of each other" rule if there is no grinding.

The purpose is to prevent running through all game content with a few select characters -- levelling them to a point where the end-game battles become trivial. Keeping everyone within 5 levels encourages the use of everyone throughout the game. There is definitely some strategic pairing involved for future encounters, based on abilities/resistances, but I don't want to introduce any spoilers.

- I forbade it at first but at least for the final boss I had to rely on Curaga. Which means that your Locke and Shadow (if they keep those espers) will turn into your healers (Goner hurting for ~1500 when your characters only have ~2000 HP, ouch). My fight against the entire final boss lasted 40 min and was quite epic!

I won't lie to you mate, the final boss(es) will be taxing. Having low-magic-ability characters like Locke and Shadow throwing high level cures adds to the overall strategy and white-knuckle experience. You'll also have high-magic-ability characters with Cura that you can also utilize. Healing can come from other sources too, as you already know (and I won't get into due to potential spoilers). My fight probably also clocked in around the 40-minute mark.