1. Some people say that it does, I myself just enjoy the feeling. But their isn't really any proof it does anything. maybe you could have a hot shower and sweat some of it out of your system.
2. Boxing your bathroom is a terrible idea. It'll stick up towles and any fabric it could even turn things white to yellow (that is bad). Smoking a joint in the shower is great though, just keep it and your arm and face away from the water. If you have a window out the window would be smart, and the steam would help cover it, then you could spray an air-freashner to aid to the effect. A pluss side is the fact that you get to be clean and not smell like it.
3. Well judging by the fact that you wouldn't wanna get cought, your best bet is to buy 8ths at a time, and smoke as needed, if you rebag this weed and smoke an a regular bases (every day or atleast once a week) then your herb is fine. I get a few OZ.s and jar that, and smoke as needed (I'm a light smoker) and it lasts me just fine.
4. Like as said, you need to be 18. Some place might not check you (but tha is very rare). As suggested just get an older friend to do it; or a family member would be better. Like a cousin.

Also when you ask about a piece, do you mean pipe or bong? Or something completely diffrent. There are plenty of guides on how to make perfectly great home-made bongs/pipes/anything. (heh). I have a home-made bong made by my cousins. Kinda got it at a party for a drink. I modafied it so the bowl is a bit bigger, and it works great. My dad used to use normal bongs, but now works with a tropicana bottle and a few 'minor' adjustments. He tells me that he won't turn back to normal bongs due to this portablity (take the add ons and top with you, and buy juice where ever you are). It's also fucking powerful as all hell though, he has a rather nifty not-so-home-made bowl.