1996 Ford Mustang Coolant leak and white smoke

I was driving on the interstate yesterday, and as I was driving my heater stopped working in my car, causing cold air to blow through the vents. About 15 minutes later when I pulled off the interstate, my dash lights started to dim and so did my headlights, although the engine still seemed to be running fine for about 10 seconds after that. I then noticed white smoke coming from under the hood, and as I went to pull the car off the road the engine died.

Now today I picked my car up and added some coolant, hoping it was a simple hose leak. However, when I added the coolant, there are two leaks; one leak is underneath the engine (possibly a lower hose?), And the other leak appears to be near or under the engine block. So my question is, do I have a cracked block, or perhaps a bad head gasket? Or is there a hose there that could be leaking? I was able to get my car home by adding coolant about every mile, and the engine didn't seem to be idling rough or making any odd noises. Unfortunately the thermostat in the engine hasn't worked for a little while and I fear that may be what caused the problem to begin with.