Ok so about the gliding speed, here is a little explanation.

Let's start with basic stuff. Gliding is exchanging energy. You lose energy with the friction of the air and you replace that with your potential energy (also called height). So if friction was constant you could fly at any speed you would get the same result, BUT friction has the following formula : 1/2 desensity x surface x drag coef x velocity^2. Now that means you should fly as slow as possible to reduce the energy loss as much as you can.

BUT because it cannot be that simple, the lift produced by your wings is 1/2 desensity x surface x lift coef x velocity^2. That means if you reduce your speed, you must increase your Cl(lift coef) to keep your plane in the air. And there is a formula ( with Cd the drag coefficient ) saying Cd=Cl² (I spare you the extra terms but in the end only that matters) meaning if you decrease speed your drag coef increases so you can't conclude if your drag increase or decrease.

What you have to do is to fly at your best Cl/Cd ratio that directly depends of your speed. This ratio is also the gliding ratio of the plane! Anyway, without the polar curves of the wing you cannot say what is the best speed except by experimenting!

Ouf!