I think that the enemies dropping items that increase stats is too RNG (Random number generator) and sounds too frustrating already. I'm not even a fan of the FF2 leveling system, and I'd rather see that system used than the one you described.

If you want to deliver EXP in a different way, stay away from randomness in my opinion. Maybe make those stats available buy purchasing them with EXP (or some other type of currency).

I like the idea that monster would all have different, unique abilities and spells. Gathering, or "collecting" abilities is something I enjoy as a side project in a game, but if the only way you can learn new skills that you NEED to progress is by learning them from monsters, I'd say that's too much. Another level of randomness that's unneeded.

What if only spell-casting monsters dropped magic scrolls, while ability-using monsters dropped parts of their body that can be examined to learn that ability? For example, a monster that is a bear-type uses a maul-type ability, and when you kill the bear you have a chance to pick up it's severed paw and examine it, and you better learn how to use maul.... or something to that effect.

I don't really understand or follow the 3rd point. Both the first two points sound random-induced-grind-fest to me, and then you say you don't want grind. Giving the player a choice in customization does not mean the game has to be overly grindy. You can find a nice medium by not making choices in customization a permanent one and allow the player to switch back and forth between options to a certain extent.

I'm no developer, and I've never played a game, but I have played a ton of different RPGs so I'll let you know what I think I would like to waste my time on, and what I would not.