how many computers needed for a nice ccna/ccnp home lab

I want to start working on my ccna then move on to my ccnp. My question is how many computers would make a nice ccna/ccnp lab? I have six towers and a laptop. Could I get away with using two or three computers or should I set up all six? I’m asking because I’m trying to figure out how I’m going to power everything with out overloading the circuits in my apartment.