You can activate “Macro Cosmos” even if you don’t have “Helios – The Primordial Sun” in your hand or Deck.
You can only Special Summon “Helios – The Primordial Sun” when “Macro Cosmos” first resolves. It is not an effect that you can activate at any time or more than once.
If “Mystical Space Typhoon” is chained to “Macro Cosmos’s” activation to destroy it, then you will not Special Summon “Helios – The Primordial Sun”. Because “Macro Cosmos” is a Continuous Trap Card, it needs to remain on the field to resolve.
While “Macro Cosmos” is active on the field, monsters that are unaffected by the effects of Trap Cards (like “Elemental Hero Wildheart”) are still removed from play instead of going to the Graveyard.
While “Macro Cosmos” is active on the field, if you Tribute a monster to Summon “Jinzo”, the Tributed monster will still be removed from play.
You can activate “Polymerization” while “Macro Cosmos” is active on the field because sending Fusion Material Monsters to the Graveyard is an effect of “Polymerization” and not a cost.
If you also have "Gravekeeper's Servant" active on the field, your opponent cannot declare an attack.