The only FF12 I played was for the DS so I'm not sure how similar it is in that aspect. I don't think I'm being as clear as I want to be with this lol, but I'm unsure how to put it.
General Combat - Normal attack maneuvers and combination based on buttons/keys used (Also, note to Senti, I would suggest making the game Controller compatible)
Materia Aspect - Fighting Pause when you hit button or key to bring up materia menu, menu should take up quarter of the screen. In menu, select skill/magic/summon to use. 2 ideas for targeting - 1. (This idea is new as I was thinking of "Arc The Lad: Twilight of the Spirits") All magics/skills should have an AoE, and the range (length and width of scope) should be judged on level. 2.Specific targeting using the "Arrow-over-head" method and selecting as many enemies as magic/skill was meant to hit. Summons should hurt all, and encompass entire feild in their attacks.
AI Fighting - (When not controlling certain members of party - ) Prior to going into battle (i.e. like when player is setting up skills and whatnot) Player should be able to set the general terms for his party members (including Cloud) with such values as "Upon: Enter Battle, (Character) Casts (Support Magic)" or "If: (Party Member) (Health/MP) reaches < (percentage) use/cast (healing potion/spell/elixer/etc)". Another thing would be to set styles such as "Beserker, Medic etc" for preset usage, unless you want to force players to set them up themselves. Another aspect to AI fighting would be deciding whether you want to make like Infinite Undiscovery and have Party stances such as "Focus (attack one enemy), Spread (each Party Member attacks random enemy), Etc." or to set these kinds of stances for each character along with their general terms.
AI Materia use - Similar to KotOR, you can set characters to use materia under certain terms, but if, for instance, there is a boss like Ifrit, who you want to constantly cast Blizzard on, Materia pause menu should let you select 3 to 4 materia attacks that you want your AI's to use in order (similar to taking control, casting them, then switching back to Cloud). To clarify, I'm Playing as Cloud, fighting Ifrit, I open up Materia menu, I select Blizzard and fill up 3 empty materia queue slots (meaning it will use the spell three times, which also means a cancel button could be implemented), Staying in the Materia menu, I switch (using designated key/button that would allow you to switch in battle) to Barret, select Blizzard 3 times, Stay in Materia menu, switch to Tifa, select 3 Blizzards, Switch once more so I'm back on Cloud (Because the option of exiting on Barret or Tifa would exit you into assuming that character) and exit the Materia menu and wait for all my blizzards to cast, then continue on with the battle. This would also work without casting anything on Cloud, filling up the AI's queue and coming back to cloud to take Aggro while the team hits hard.
/long explanation that hopefully makes more sense