Which data do you need to calculate the wing load?
The wing load is defined as the weight on the wing per square metre. Therefore you need the total take-off weight and the flat surface of the wing to calculate it. For example, a 25m2 glider flown by a pilot with a TOW of 100kg has a wing load of 4kg/m2.

What do we call the risers that are connected to the lines running to the leading edge of the canopy?
These are the A-risers connected to the A-lines.

You are standing on take-off and you feel the wind coming a bit from the side. Is that a problem for a safe launch?
B is the only correct answer for an Alpine or forward launch in the mountains. When you choose to execute a reverse launch, C is a possibility as well. For a tow launch, sometimes a 90 degree crosswind can be safe to start for more experienced pilots.

'Big ears' are a descent technique and serve to increase your descent rate. Additionally, in which situation is pulling 'big ears' a good idea?
Pulling big ears reduces the wing area and therefore increases the wing load. This stabilizes the canopy somewhat. It also increases the flying speed but in most cases this is counteracted by the extra drag the ears create.

Why are the cell openings slightly pointed down?
The cell openings are positioned where the air flow hits the profile of the airfoil.

For a paraglider in the mountains, what wind speeds are considered safe to fly?
Wind results in turbulence in the mountains. While soaring on a ridge or at low dunes or flying in flatlands may be safe up to 4 Bft or a bit higher using a smaller mini-wing, in the mountains a wind speed up to 3 Bft (a maximum of 20 km/h) is the maximum for most pilots to fly safely. Strong winds are considered 25 km/h or over.

What happens when you fly too slowly?
Below the minimum speed or stall speed, the wing stops flying and will descend straight down like a parachute. This is a very unstable situation and often leads to a spin or stall.
See the chapters on Aerodynamics (stalls) and Advanced flying.

How tight do you need to pull the leg straps of the harness?
The tightness of the leg straps does not influence the flying properties of the paraglider.
When the leg straps are too loose, after take-off you will find yourself hanging low under the seat and it's more difficult to get in the harness.
Too tight will hinder your movements during take-off, depending on the harness design. In some harnesses it will prevent you from getting into the seat fully.

A paraglider glides down through the air. But at what speed?
These are all speeds relative to the air!

A pre-flight check should be executed...
Before you take off, you should check at least these things: pilot, lines, canopy, wind, airspace.
Your result is shown above.