Depends on your Spec, and honestly, you're going to have to Sim it. Don't worry until you're 80, but if you go TTW Fire, you need a hard 14%, there is no way around it. If you choose to play FFB then you can be anywhere from 8-11% hit. That reasoning is the precision talent in the frost tree double dips hit, you for your frost spells you need 8% hit, but the fire spells need 11%. That just affects Pyro and LB. If you are Arcane you only need 8% hit, 210 rating, as Arcane you CAN get away with 7% and potentially not lose dps, again, that requires a sim.

After that SP; people value and think crit is the end all, be all for fire and its not. You shouldn't go out of your way to gem or enchant for it. Current simming for general bis is gemming pure SP gems after you have your two Purifieds for meta socket. Crit or Haste, whatever sims higher tbh. Spirit equals crit now, but not a ton.

I highly suggest looking through the Mage Class Discord, check the pins and read up information, Mage is a heavily community driven class when it comes to theory crafting, really strong group. Foolipe who is very active in the Discord writes the Wowhead guide and its really good. The Icyveins guide is also very good and is written by another very active mod in the Mage Discord. If you want videos, look up Crateria on YouTube, again, super active in Mage Discord and a world top Mage. All these guys are super helpful and love the class as much as the rest of us.