#1
why are 1st inversions marked with a 6?
6th chords themselves arent inversions are they?
#2
Quote by thunderkix
6th chords themselves arent inversions are they?
No, they aren't.

They are marked with a six because the interval from the "bottom" note to the "top" note is a sixth (3rd to root octave).
Only play what you hear. If you don’t hear anything, don’t play anything.
-Chick Corea
#4
That's a figured bass marking. If it says 6 or 6 3 then it's in 1st inversion, 6 4 would be 2nd inversion.