Glider Weight/Wing Loading and determing speed for best L/D for a given weight

As a fairly new transitioned glider pilot I am interested in
information concerning wing loading and determining the speed to
achieve best L/D and effects on Minimum Sink

I think I have a basic understanding of the effects wing loading has on
the flight of the glider. The heavier the wing loading the move lift
needed to climb and the climb will be slower than a glider with light
wing loading. Once the altitude is gained the heavier glider will have
the higher speed between thermals as long as the correct speed for the
weight of the glider is flown.

I am also researching the used glider market for one day purchasing a
glider.

Which leads to what I am asking here. Is there an optimum wing loading
that is the best middle of the road for performance? And, which
gliders would exhibit them; LS3, LS4, ASW 19, DG300, Mosquito for
example?

What weight is used by the manufacturer to determine the wing loading
when it is published? All up max weight or some other arbitray value?
What weight is the glider flown at when the manfacturer is determining
the polar?

Once you have determined the weight of the glider How do you determined
the airspeed for best L/D and min sink?

Or, is this all non-issue?

Thanks
65E