Somewhere around 2/14 These are not rules of thumb, these are MHO's:
plate == base of speaker -- I don't like overhang, because it seems less stable, but neither do I like the plate to be bigger -- the speaker baffle should not have any additional reflecting surfaces right there.
Construction == should be stable, inert, etc. (seems rather intuitive, not sure what you're looking for here). Shouldn't ring -- basically, same rules as would apply to the speaker cabinet.
I like three legs (as opposed to one, two, or four, etc.).
Most of the magazine writers swear by sand-fillable. I don't, but that's me.