FoxWander
Adventurer
Well first off, do you have any feats or class abilities that would let you put a Metamagic Enlarge on a 9th level spell? Cause with Genesis your Demi-plane would only be 340 feet across. Kinda small for a whole "plane", dontcha think. But Enlarge could work on it since it's area is defined by its range. Anyway, get a bigger demi-plane if you can.
Even if you can I wouldn't make it a negative energy plane. Sure your vamps may love it but do you really want to fall into the cliche bad guy idea of requiring a special item (negative plane protection) just to survive in your own "Fortress of Solitude"?
I'd make it perpetually night, sure- but not negative energy. Unless your gonna go vamp yourself, in which case- go for it!
If your looking at this as your ultimate safe getaway, then the ultimate deathtrap dungeon right at the physical entrance would be a must. Engineer the place with solid adamantine natural geography in a convenient "Ultimate Fortress" shape. Then cover the place with Unhallow spells so your vamps are happy.
Oh, and don't forget the sharks with frickin laser beams on their heads! (or for D&D that'd be Dire sharks with frickin wands of magic missile on thier heads.)
Even if you can I wouldn't make it a negative energy plane. Sure your vamps may love it but do you really want to fall into the cliche bad guy idea of requiring a special item (negative plane protection) just to survive in your own "Fortress of Solitude"?

If your looking at this as your ultimate safe getaway, then the ultimate deathtrap dungeon right at the physical entrance would be a must. Engineer the place with solid adamantine natural geography in a convenient "Ultimate Fortress" shape. Then cover the place with Unhallow spells so your vamps are happy.
Oh, and don't forget the sharks with frickin laser beams on their heads! (or for D&D that'd be Dire sharks with frickin wands of magic missile on thier heads.)