LAST STAND

Does this Attack benefit from the Abilities of any Attachments in the unit?

Yes, assuming they were destroyed by same Attack/effect that triggered the destruction of the unit.

If I perform an attack with last stand and destroy an enemy unit, do I get to Surge Forth or Overrun?

No. Destroyed units may not perform actions unless specifically allowed to by an ability or tactics card. See General section, Destroyed State.