From a fresh start with no upgrades I get the following achievements-
'In a league of their own' for getting above 1 million points.
'Never Knew what hit them' for getting silent assassin.
With the following Challenges-
'Hidden Tiger' for hiding all the bodies.
'Pink Mist' for scoring all headshots.
'Cold War' for hiding five bodies in snow.
'In the cut' for hiding targets.
'Fusil for everyone' for hiding body in the riot.
As long as you take out the bodyguards and target to begin with you can take your time. Watch for the fat bald target to head towards main building, The guard and his buddy near the lower area can be awkward.