I'm trying to imagine life in this kingdom, ruled over by its immortal vampire tyrant queen (whom presumably everyone knows is a vampire, but nobody is willing to say out loud) who really has a thing for throwing big hammers. Oh, and she's killed about 3000 of her people over the years.
You'd have people both serious and ironically saying things like "Ontha does nothing wrong".
How successful is it compared to other Kingdoms?
Aside from her are there any dangers?
No other major threats. The only wars this civ has ever faced are civil wars (of which there have been several). One of the more interesting was a subgroup called the Society of Chancing, which held out in a 120-year long war against The Saturnine Group (which appears to be the predominant group in the civ; Ontha is a member, as are the other major civ figures, such as the war-leader and a vampire general, Thram Fleshruled).
In 113, the war began with a skirmish when a group of 135 from the Saturnine Group, led by a vampire, attacked the Society of Chancing's lone settlement, defended by only 8 people. The Saturnines lost 85, the Society lost 5. And the day was won by the Society. The conflict was over grazing rights and livestock ownership.
In 194, the Saturnines launched a second assault, this time with 497 against 11. The Saturnines lost 380, including all 371 unnamed humans, while the Society had a lone survivor, Accok Sombercudgel, a Great Lasher.
In 237, the Saturnines launched the third and final assault, pitting 1021 against 12. The Society was annhilated, but the Saturnines lost 824, including all 820 unnamed humans.
I picture the Society of Chancing as this tiny band of badass dissident vampire slayers, refusing to live under the yoke of Ontha the Hammer-Queen (as livestock), and every few generations winning a Pyrrhic victory by wiping out hordes of Ontha's thralls in a desperate From Dusk Till Dawn-style melee, until at last there were just too few to hold back the tide. Also worth noting that in the third assault, the Saturnines had brought a number of giant animals with them in their warparty. Accok, the lone survivor from the second battle, was actually slain by a two-humped camel, while the leader of the defense was slain by a giant skink. Two of the other named humans in that final battle were children of one of the fallen defenders from the 2nd battle.
Vampires have formed a surprisingly large percentage of the noble positions in The Saturnine Group over time, even as there have been a number slain in vampire purges.
I genned up another world with a shorter history, and found a similar situation: human civilization with a vampire law-giver, annual athletic competition (wrestling in this case), and the vampire being the annual champion, in part because no one has competed with them for decades.
I'm tempted to gen up some 500- and 1000-year worlds and test a hypothesis:
As the length of a human civilization increases, the probability of their leader being a vampire sports buff approaches 1.