Re: Harsh Shisha and foil question
If the smoke isn't good, it's not a waste at all, just disposing of bad stuff.
And even if it were, given the number of inhales worth of smoke in a session, I wouldn't worry too much.
As for your foil question, I don't prefer using two layers of foil. I find that it usually requires too much heat. The better option is to buy some heavy duty foil, which is a bit thicker, and thus helps prevent burning the shisha. But it's worth trying two layers; with your rig, shisha, and coals, it may work out perfectly.
Another thing to try is making sure that your shisha isn't touching the foil. This is more important with drier shisha than wet shisha. Wet shishas like Tangiers actually smoke better if you pack the bowl right up to the foil. But if you're having troubles with burning your shisha, this is a good trick to try.