With a CTN of 29, that would mean that it requires 5 Spell Points to cast, which in turn means that the Save would have a TN of 19 (14 + 5 SP = 19)
As for the cost of the steps leading to death, I have no problems adjusting them as they might need to be adjusted through practice (afterall, that was basically mad up as I typed it up, so likely DOES need tweaking.... I would go with 5, 9 and 12 to start with..., and then increase the duration effects by 2 points across the board... (i.e. 6 rounds would be 2 points, 2 rounds would be 6 points, etc..)
I would also suggest that for such spells, that the target is Stunned, for the entire duration of the spell (until the death hits)....
So, with my suggestions, that would make the CTN be 36 (12 base + 12 death + 6 death in 2 rounds + 2 range of 50' + 4 special penalty if Save is made) which means 10 points to learn (for non-caster, 9 for minor adept, 8 for major), and require 7 spell points to cast, and the target would get a Save vs TN 21