I have several electrical questions:

1. Is it allowable to connect 12 gauge wire to a 15amp breaker in the
service panel ?

2. How many half height single pole breakers are allowed in the main
panel rated for 200amp ?

3. I noticed something very interesting in a 3-way switch arrangement
in my home. To power a receptacle, they grabbed an unswitched feed
from the light fixture by connecting a black wire to both travelers in
the box. Since there is always power on exactly one of them, this
seems to work. Is this allowable ?

4. Is it ok to wire more than 4 receptacles downstream from a GFCI
outlet ?

Thanks...