I'm gonna have to disagree with Estellios.

I put MP into every slot possible. Adding large amounts of MND or healing potency gear doesn't seem to have a significant effect on how much HP gets healed - at least not nearly as noticeable as healing someone with or without Prime Conditioning.

Higher max MP definitely increases the amount of MP gained from Tranquility. I believe it also increases the amount of MP you regen by standing still. I also noticed that MP food such as Pumpkin Cookies gave me higher bonus MP when I upgraded my gear with more MP materia (+50 mp -> +52 MP). So MP food is probably percentage-based.

With Full Party and food I have about 1560 MP. Another mage in my LS has double-slotted MP materia on all gear and gets around 1680 MP. Oftentimes, we'll get to Hellfire on Ifrit with 80-90% MP remaining with Tranquility still up. That's like 300-400 more effective MP during phase 5 than a mage that does not slot MP.

I also feel that -Enmity is not worth it. In long fights, Accomplice makes hate management trivial. In shorter fights such as beastman strongholds, I find that taking hate is largely dependent on what actions you take. Use Stoneskin and single-target heals on MRDs spamming Storm's Path and you shouldn't pull hate. Use Curaga early on and you will always pull hate. If necessary, Curaga and activate Sentinel along with a few shield skills since mobs die fast anyways.

In any case, gear to consider:

Wand: Wand of Gales
Staff: Jade Crook (M.Acc) / Ifrit's Cane (M.Pot)
Shield: Eagle-Crested Round Shield or Square Ash Shield (M.Acc)
Head: Felt Hat Green (M.Acc) / Electrum Circlet Rubellite (MP+Fire Resist) / Mask of the Mortal Hex (M.Pot)
Body: Felt Robe Red (MND) / Felt Robe Green (M.Pot)
Hands: Boarskin Ringband of Gales / Leather Mitts (MP)
Legs: Felt Gaskins (Brown)
Waist: Raptorskin Satchel Belt
Feet: Peisteskin Crakows Red
Accessories: Blue/Red Coral Wristbands / Black Pearl Rings

Materia to consider:

Wand: MP or Healing Potency
Staff: M.Crit
Shield: HP+MP (Lifethirst)
Head: MP or Healing Potency or M.Acc
Body: MP
Hands: M.Crit
Legs: MP
Waist: MP
Feet: HP or M.Eva or M.Potency

MND and enmity don't do enough to justify the slot. Healing Potency still needs to be proven. Magic accuracy can be useful (Slow and Blind on Ifrit will save a lot of MP), but how much of an effect this has on land rate remains to be seen.

MP is the most universal and a safe bet (probably the cheapest too). Feet have bad choices for mages so get whatever there.