and there won't be a campaign there, only a map appears - Heart of Nightmare. You need to play it through a single skirmish - scenario. Additional campaigns are only available in DLCs. The main campaigns appear after completing the very first one for Vyacheslav, and the final one is unlocked after completing one regular campaign.

Added 1 minute ago

I don't see the point in buying the gold edition just for the exclusive map.

If the complete edition includes the unique weapon, the Staff of Saragret, and the Dragon's Tongue, I will definitely buy it and won't regret spending the money.