If you don't need the extra low frequency bass, multiple 500s will give you more options. You could stack them or split them apart.

Heck, on days where you want to be an adult, move them apart and enjoy equipotential bass as you graze(TM). On days where you want to be a teen, stack them and dance your face off in the centre of your room.

As for the feet, I would say experiment. I'd be worried about bass being coupled to your platter.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated