"A target with total cover can't be targeted directly by an attack or a spell... A target has total cover if it is completely concealed by an obstacle." PHB pg 196
"To target something, you must have a clear path to it, so it can't be behind total cover." PHB pg 204
Mage hand appears at a target location within range. Wall of force should stop spells based on cover (regardless of lack of obscurement). As long as there are no openings for the hand to float through it should be good to disallow.
No. The hand does not need to float through the wall, it appears out of thin air on the opposite side and nothing is arrested or arrestable by the wall or any other wall to stop the caster from moving the hand. The cover rules apply to attacks with arrows and such, where a projectile or bolt of physical energy like fire or lighting needs to travel to the target. Being really technical, so long as the caster can see where he or she wants to place the mage hand, nothing is moving that could ever be stopped by a wall.