You wrote:
“ ‘ m = E / c^2 * sqrt( 1 - v^2 / c^2 ) ’
So for fixed energy,
the mass goes to zero as speed approaches the speed of light. ”.

“ Mass** ” goes to infinity as v approaches c:
“ Mass = Energy * c^-2 * ( 1 - v^2 / c^2 )^-.5 ”.
** i.e. “ Relativistic Mass ”,
not “ Invariant Mass ”, not “ Intrinsic Mass ”, not “ Proper Mass ”.