[Radek]

Some hints:

1. Use only "400 souls", that means souls of Golden Saints and Ascended Sleepers. You will need grand soul gems or the Azura Star for it.
2. Start with adding the cheapest enchantments. Note that every new enchantment doubles the price of all already added enchantments.
3. Consider adding a short term Soul Trap "cast when strikes". Your weapon will try to catch every soul it hits. A few seconds (say, 10) is enough. Note that the weapon will strike again and again so that the Soul Trap will be reset again and again.
4. When you add a magic bonus attack (fire, etc.) then do not forget than many creatures have 20% Spell Reflection. It's an ability, not a spell, therefore, the monster need not cast it and the Spell Reflection will never wear off. Select an element, which you are most immune to. Otherwise, the weapon can harm you seriously.
5. Add a healing spell cast on you yourself "cast when strikes". It's possible. The weapon will heal you with every strike and make you almost unkillable. Note: pure heal is better than lifesteal. It's cheaper and do not forget the Spell Reflection.