All right you can not buy sorcerery or necromancy spells. There is a character that can use them. The Red Mage, but he’s a temp character. Having him join you can be a bad thing.
As for Pillar. Some say you must have an evil point already for pillar spamming to gain more evil points. Also if you learned of the location of “Saruin” from Trials of Elore or Aldburg before hearing the “Tale of Death” from the Minstrel you can never hear it in that quest. In order to gain at least one evil. First you must be Hawke, Gray or Jamil as they start with some. If you are none of those characters then do one of the following. Kill Wuhan, Kill Galahad, Kill an Elemental Lord, Complete Soul Gutter Quest or get the Obsidian Sword. There may be more than that.
To preform the pillar, I believe it’s a three person combination. One person must be in front while the person on his left and the person on his right must be in the middle row. If you can find three attacks that combo together and such then you have a chance of pillar coming up. Some have said pillar only raises points once per battle. So if you get it to appear once in a round don’t worry about getting it to appear a second time or whatever in the same round.
Advice for you. Once you find your combination rely on fixed order. This way you can make sure the members attack in the order you want increasing the chances for a combo and hopefully Pillar. I also make sure the two not involved in the combo attack a different enemy or heal as to avoid messing up the combo.
