15 Amp Single-Pole Toggle Light Switch, White

If you check the manufacturers installation instructions, they specify the use of copper or copper-clad wire only. Aluminum requires a much larger diameter (almost twice the size) to carry the same current as copper. If the existing wiring is aluminum, I would consider a rewire with copper; it is smaller, lighter, and more compatible with products offered today.

Well, let's do the math. The switch is rated at 110v (RMS) with a maximum current of 15 amps. V x A = Watts 110 x 15 = 1650 watts. So, the answer is yes, but barely. I would suggest getting a high power 20 amp switch just for a safety cushion.

Yes, it will

#6-32 thread. That's number six, a more or less random diameter number, With 32 threads per inch. The Most common larger head diameter is called "pan-head"

If your switch plate has the standard rectangle small hole, it will fit

Certainly. Just because it's made for higher voltages, 110 V or 120 V, that doesn't mean it won't work at the lower voltages used for speakers.

Yes I used it to turn on a air compressor. Pretty sure it can make popcorn

Generally, screws of this size are not supplied with a specified torque, because most people don't have an appropriate torque wrench. Also, you have not specified whether you are talking about the terminal screws or the mounting screws. I assume you are talking about the terminal screws. I sympathize with your lack of torque spec, and I agree that it should be specified for best results, but I doubt that any electrician ever uses a torque wrench for these. You might be able to find the torque spec if you go to the manufacturer's website, but even there it's doubtful that they will supply it.

I use it on 120 volt lines. I have no problems with it switching LED lighting.

The other problem with non led compatible switches are that they bleed a small amount of electric. I do have Leviton switches that do not fully shut off led lights. In a dark background you will see that they stay lit. Like led rope lights or led string lights. A standard 120 volt on off switch can bleed 2.5 volts that can allow led lights to glow.