So I think I did the enhancement bonuses correctly... And I assumed an H to be safe. Let me know if something needs changing.
[spoiler]5. Pay
6. Turn Undead
7. Pay
8. Rebuke Undead
9. Pay
10. Fort save v. Blindness on crit (10+1/2 level+Int)
11. +1 weapon
12. Pay
13. Add Modified Vorpal Quality
14. Pay
15. Soul Compulsion (Use a class ability as the soul could, switchable as a Full Round Action)
16. Soul Control (Use their ranks in Int based skills)
17. Pay
18. Add Shadow Striking Ability (ToM)
19. Pay
20. The Reaper's Grace (Incorpreal subtype with non of the drawbacks)[/spoiler]