Before we begin...
There is a MAJOR problem with soul shards management early on: once you hit the “Spirit of Nightfall” feat you will basically generate as much shards as you will at lvl 80 except you almost won’t have things to spend them on. This is one of the reasons why people go Lotus over Corruption for the early game.
this is how you spend your points:
Improved Unholy Stance -> Corruption Strikes -> 1 point in Spirit of Nightfall -> Unholy Strength -> 2 points in Dark Weapon -> 2 points in Spirit of Nightfall -> Necrotic Leech -> Vampiryc nature -> 1 point in Dark Weapon
Lets go over your feats:
Your main “shard eater” up to lvl 30. Gives whooping +20% offhand buff and has a low cool down. Buff yourself whenever you can.
+10% damage boost for you swift strikes (SS) combos. Passive and great.
Spirit of Nightfall and Dark weapon feat dancing
As you could tell I did quite a bit of feat dancing with those. There reason before adding one point in SoN early on is to generate more shards while not generating too much of them. Dark weapon gives nice damage boost so you will benefit more from having just one point in SoN early on and with added damage from Dark weapon than having fully upgraded SoN, lots of shards sitting in your UI and no damage.
Both, vampiryc and necrotic are considered “leeches” meaning they will give you nice health return for the damage being done to your enemy. For best results use them both at the same time on bigger group of mobs.
Your survivality suffers when you go corruption early on. You have NO defensive feats and all you can do is “SPRAY AND PRAY” the crowd hoping for the best – Lotus is clearly superior in that sense.
No points in Life Leech?
Life Leech doesn’t scale so sooner or later you will find it doesn’t give enough back for 5 points invested. Word in the assassin community is – Life Leech sucks.
There are none. Corruption is pretty straight forward.
Shards burning aka Consume souls
If you cannot use the shard because of cool downs on your shard using feats – burn them with consume souls for that sweet stamina boost. More stamina means less down time.