HITMAN World of Assassination

Not my video, but it is the fastest, safest, and most efficient. Although it is only for level 5, it should be useful for levels 1-4 as well because it shows you the fastest way to get the items/disguises required.

To find this mission, go to the Destinations tab. Then scroll left, select ICA facility then The Snorrason Ascension.

The Einarsson Inception
Level 1: Eliminate Evan Holden with a kitchen knife while wearing a yacht security disguise.
Level 2: Additional security cameras are introduced, increasing the difficulty of staying undetected.
Level 3: Take down Terry Norfolk while disguised as Yacht Crew.
Level 4: All Yacht Security NPCs can now see through both the Yacht Security and Yacht Crew disguises.
Level 5: Complete all objectives within a strict 5-minute time limit.

The Snorrason Ascension
Level 1: Your mission is to eliminate Cilas Netzke while wearing a soviet soldier disguise using a pistol.
Level 2: In addition to eliminating Cilas Netzke, you must break into the safe and steal its contents.
Level 3: Now, you also need to eliminate Moses Butusov while disguised as an Airplane Mechanic.
Level 4: On top of previous tasks, you must hide all dead bodies within 30 seconds of their deaths.
Level 5: Lastly, you need to complete all objectives without pacifying anyone.