Unfortunately, Quark is mine-able with the GPU using Smelter (https://bitcointalk.org/index.php?topic=310975.0) so this will be too. I know a few people that are using it with a couple topmid-high class GPU's and getting near the same performance of the highest desktop class processor you can buy.

You could change the hashing and keep it closed source if you have the know how, this would deter GPU miners and* keep it slightly fairer I guess... Although, that being said, the majority of the people I know whom are mining are using CPU only.

Moreover, is it possible you can have at least one pool and a block explorer ready up before launch? This will help greatly, as you'll get many people asking straight away. (=^･^=)

Edit*: Typo