No,I doubt Nathan set his dads place on fire. I mean he's still pissed at Lucas for hidding stuff about his dad from him.I think it might be Keith that set it on fire.Deb is surely the one who poisoned the drink.
I don't think Peyton's mom was buying drugs though.I think she was getting information on Peyton even though it was a really small thing she put in her pocket ! i dunno.Did deb dissapear??she had a relativly short appearence in ep1. and in ep2. i don't remember seeing her.