So...here is the problem with your comp. You should have at least one champ with three items at the min. You put most of your items onto almost all your champs. You should have focused on one of your assassins to make them the leading power house. Zed, Kha'zix or Pyke would have been your better choices, but you can turn Katarina is a powerhouse if say you made her a sorc assassin, uping her ap and giving her a hextech for example. If you wanted to run around void, you should at least give them ap damage as that's where most of their true damage comes from. It's not so much the comp, it can be the item comp.
The problem generally with assassins from experience running them is you almost need something to off set their strength. Having a tanky sort of comp around them a bit. While if you wanted to continue to void, I would have exchanged kassadin with cho'gath and still have rek'sai, which would help a bit. Otherwise running a bit into knight or guardian (mostly knight) would help with the assassin comp giving a bit of that block damage. You could also run slightly into yordles, but since yorlde's buff only applies to yordles, it wouldn't be ideal where knight would apply to the entire team.
If you wanted to go pure damage, it would be risky, but assassin gunslinger isn't too bad. Same with assassin blade, but I find assassin blade to be a bit harder.