It's your project and you can call things whatever you like; still, the 8 free cores seem to me more like a "horde" than a "hoard".

Generally things hoarded are sequestered on a shelf against some imagined future need instead of put into service. At the same time, a "horde" usually numbers more than 8, except when treated ironically, after the manner of "three's a crowd". So I would suggest "horde", or "crowd". 8 is just a bit thin even for a crowd, unless it concerns a certain president's inauguration attendance.