Tail Rotor Roll
If the tail rotor is below the level of the main rotor, the drift mentioned above will cause a couple with the tail rotor thrust going the other way, causing one or other of the skids to be lower in the hover, depending on the blade rotation (it's the left one with North American rotation, that is, anticlockwise as viewed from the top). It is therefore totally normal for one skid to be lower than the other, unless you've left the refuelling hose in (actually, this characteristic is quite useful when landing on sloping ground, as long as the slope goes with the skids).
To combat this, you could raise the tail rotor on a boom or lower the rotor head, as is done with the Brantly, but the C of G position could screw that up anyway.

Rotor Systems

Three or more blades require a fully articulated rotor, which essentially allows all of them to move in their various planes independently of each other. This adds complexity and expense to the design, however.
A semi rigid rotor has the blades fixed with regard to feathering, but they can flap up and down because the whole head is allowed to teeter, like a seesaw.
A rigid rotor only allows feathering, but the blades are more flexible towards their ends, so they bend when absorbing the forces of flight, producing the same effect as flapping and dragging hinges, but removed from the root. This is why some helicopters have mast torque gauges to measure the bending of the mast.

In flight
In the hover, other things being equal, the lift vector acts directly upwards:

When you tilt the disc forward, the lift vector is reduced, because some of it is diverted towards the direction selected: The resultant (i.e. the diagonal line drawn across the two vectors) is where the main force finally ends up.

The tangential velocity is the speed of the blades' rotation. It increases with distance away from the hub, until it finally becomes a tangent to the edge of the disc, hence the name:
Combined with the downwash velocity, you end up with a resultant corresponding with the blade's actual speed and path, or the relative wind (although its name suggests otherwise, the downwash component moves upwards).