4.  How do I know what is “good” art?

"Good" art is anything that moves you.  Whether it makes you happy or solemn or leaves you in awe, it is doing it's job.  Art is completely subjective and no formula can be used to determine a quality piece of work.  What you love intensely may be ugly to someone else.  Many of the most moving and innovative works of art come from budding artists who are as yet unknown.  A famous name or a certificate of authenticity will not make a piece more exciting to your eye, nor will the lack of them make the piece worthless.