#1
What are all the chords that are in the key of Am/C. My band wants to create a song and I want to know my options. I do not know too much theory. I know the major/minor chords in that key but wanna know the intricate ones two like sus and 9th and 11 etc. Thanks.
#3
Any chord that contains CDEFGAB.

To find out whether a chord fits into the key of C major, look at the notes it contains and see if they appear in the C major scale.

Eg: A G11 is in the key of C major because the notes it contains (GBCDF) all appear in the C major scale.
A B11 is not in the key of C major because the notes that make up a B11 (BD#EF#A) dont all appear in the C major scale.