I've always wanted to play a magic thrower and I'm wondering what spells would best compliment throwing? White necromancy of course, but what else would work well?
The big one would be Hasten, the third Temporal spell. It doubles your speed, which gives you almost twice as many throws in turn-based mode. Tempus Fugit, the final Temporal spell, improves speed for your entire party, but costs more to cast and maintain.
Similarly, you can cast Agility of Fire one or more times upon yourself (it stacks) to boost your speed. If you get your DX up to 20, you even get an additional +5 speed bonus. Hasten still doubles this, so in a sense it stacks as well.
After that, you just want to research enough spells to get your MA to at least 75, to get the most out of the Enchanted War Boots you'll be buying (more speed bonuses!) and the weapon you'll eventually get from the Throwing Master's quest. I personally like Conveyance (Unlocking Cantrip, Teleportation), Divination (Sense Hidden is as good as Spot Traps mastery), and even Purity of Water (for bartering in towns). But your mileage may vary; maybe you'd prefer Black Necro instead, or Summoning, or Mental.
Also remember that the ST bonus does not apply to thrown weapons, so if you decide not to invest points there, casting Shield of Protection is a good way to boost your AC without killing your encumbrance by wearing something too heavy. Keep in mind as well that maintaining too many spells can be quite fatiguing; you may want to invest in CN (faster recovery time) and/or stock up on Greater Fatigue potions to replenish yourself as you go.