This seems to be the last hangup for me on my build. I'm a new builder and therefore don't know how significant the difference will be between mid and full tower cases (of course I can always gauge it by the measurements...but relative to what's going inside I don't know if the lesser room will be a problem).
I'm not building a gaming rig. I'm building a rig capable of working well for my wife and I, able to be updated for years to come, is efficient, and just works well for general purposes. Therefore I'm not getting a big graphics card, my hard drive is is a Western Digital "Green" (energy efficient), and I won't be overclocking, so I don't expect a lot of heat. But for a full ATX motherboard, will a mid-tower be fine?
I'd like to keep it to a mid-tower if possible just to save on the budget, but if I'm going to screw myself over please tell me. Thanks!
A mid tower is fine. Just ensure that whatever you get will be easy to work in, and isn't too cramped. ie a micro ATX system is probably going to far in the other direction, unless space is a significant concern.
Based on your description, am I right in assuming that you want a fairly silent system? If so, I'd suggest replacing the stock CPU heatsink with an aftermarket product that has a larger fan. For moving a given volume of air, the larger the fan, the more quiet it is. However, this does impact on case size-the heatsink will take significantly more room. This is another reason to recommend a mid-tower over something smaller.
Mid-towers can also support more fans, and are therefore quieter-the fans can run much slower.
I have a large mid-tower with an i5, and both the CPU and graphics card are overclocked. It has 5 case fans, a CPU fan and a GPU fan. At idle speeds, you can't even tell the computer is running. It only ramps up when playing games.