I've only played Tien Chi for about 20 turns, but taking a quick look at their recruitable mages...
Air: Your Celestial Master can rarely get 3 Air, but I wouldn't rely on it. If you want to be able to forge boosters without empowering put 4 Air on your pretender.
Astral: Your Celestial Master can rarely get 3 Astral, and they can more reliably get 2 Astral and 1 Earth (give them Earth Boots and they can forge a Crystal Coin). If you're willing to take the risk, you can skip Astral on your pretender. (Celestial Master with 3 Astral + Starshine Skullcap + Crystal Coin gets you to the important rings)
Blood: You have no blood access, but I rarely put blood on my pretender. There are more important things to do with your pretender than blood hunt.
Death: You only get 1 Death, so you can take some Death on your pretender or you can wait until you forge a Ring of Sorcery which boosts you to 2 which is enough to work your way up from there.
Earth: Master of the Five Elements get get an Earth pick so they can forge Earth Boots and a Dwarven Hammer, so you don't need Earth on your pretender.
Fire: Your highest Fire level is 2, and you cannot get a Death/Fire pick. So put 4 Fire on your pretender to forge the Flame Helmet, and 1 Death for the Flaming Skull.
Nature: You can get up to Nature 2, or Nature 1 and Astral 2 or 3. Unfortunately you're just short of a Moonvine Bracelet, so it wouldn't hurt to put Nature on your pretender.
Water: All your mages can get Water 2 or more, so you're set here.
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Taking all that into account, I would say go with a rainbow pretender with:
Air 4
Astral 4
Death 2
Fire 4
Nature 4
You can definitely get away with less, but you probably don't want to rely on the 10% Astral pick from the Celestial Master, and an extra level here or there keeps you from jumping through too many hoops and provides a nice cushion. You also get multiple weak blesses for your sacred mages.
So if you pick a Crone as your pretender you are left with 14 points after all of that. This means you need to take some negative scales (sloth or misfortune) or put your Crone to sleep if you want a Dominion higher than 2. She doesn't have a torso slot, but you don't necessarily need it and she can wear 4 accessories.
If you have any other questions, don't hesitate to ask.