The Vor'cha costume is simply a skin for a ship that you can buy for energy credits. It doesn't unlock an entire ship. There are also skins for the Advanced Escort, Fleet Escort, Assault Cruiser, Deep Space Science Vessel, and Reconnaissance Science Vessel,
These skins are basically costume pieces, similar to the uniforms you wear on your character.
From the C-STore:
Klingon Empire - Guramba Siege Destroyer
A Nausicaan ship conscripted for use by the Klingon Defense Force, the Guramba embodies the Nausicaan ideals of strength and power. The Guramba Siege Destroyer has seven weapons slots (4 fore, 3 aft), seats for five bridge officers (Lieutenant Commander Tactical, Commander Tactical, Ensign Engineering, Lieutenant Engineering and Lieutenant Science) and space for eight console modifications (4 Tactical, 2 Engineering,… read more 2 Science). It carries a crew of 300, and can enable Siege Mode, which transforms the ship into a battle configuration. Siege Mode diverts power from the engines for more powerful attacks. In addition, each use of energy weapons in Siege Mode steals power from enemy vessels to power the massive energy javelin that is the Guramba's most powerful weapon. When the javelin is fired, the ship will return to its normal configuration. Note: This ship may be purchased only by Klingon Empire captains that have attained the rank of Lieutenant General. Purchasing this ship from the C-store unlocks it for all Lieutenant General characters on an account.
You would need at least one KDF character at the Lt General rank to be able to purchase this ship as per this listing. I hope this information helps.