For the sound activated lights, there are kits that I've seen in stores that turn assorted lights (like black lights, etc.) on and off based on sound. They're usually inexpensive and should be relatively easy to wire an input into for the mic. They tend to have sensitivity controls, too.
Depending on the voltages, it shouldn't be much to just swap the speaker in with mic in. They're both inputs. Granted, there are things like input impedance and matching voltages to think about, but the math will be simple to figure it out.