Since you're working for a non-profit, I'd probably concentrate on keeping licensing costs down, so, as few servers as possible. While you can split your databases across multiple instances, you then have a lot of overhead for each instance and you'll be managing memory in ways that are, frankly, a pain. I'm pretty sure I'd go with two servers as you already have. Some of the second-tier systems on one and the more important systems on the other. These are all very small databases, so I'd probably keep them all in a single instance. The one real trick you can do is to get more drives and drive controllers involved in this to spread that load as much as possible. Also, 64-bit so you can add memory as needed (and the correct amount of memory is either "All of it" or "More").