For that many nodes you should be ok to put SQL on the same server as NCM. That is provided that you are installing NCM in a standalone deployment and not integrating it with NPM.
According to the NCM Admin guide the minimum requirements are for a dual core 3GHz cpu with at least 3 GB of ram and 20GB of free disk space. You should be ok even with a 2.5GHz cpu, but I'd recommend 4GB of ram or more. And if you can allocate a quad core, all the better.
http://www.solarwinds.com/support/orionNCM/docs/orionNCMAdministratorGuide.pdf