Thanks
Geemo!
OP, I generally agree with
Geemo that the earlier you can go the better. Early October has several events happening in and around the parks and extremely high crowds are pretty common, especially on the weekends (Fri to Sun).
At this point, we don't know what the entertainment schedule will be like in October (they're doing some different things so far this year), but historically, the do not present fireworks on weekdays (Mon to Thu) during the non-peak season. So if you wanted to see
Disneyland Forever, you'll want to include on Sat or Sun evening to be safe (they would normally also present fireworks on Fri nights, but I'm guessing there will be a MHP on all of the Fri nights during your time window). Again, assuming that 2016 is similar to 2015, DL hosts Mickey's Halloween Party (a special ticket event) on select nights in late-September through Halloween. Based on the past, there is likely to be several parties during your time window. I would highly recommend looking into the party, but if you don't want to go, note that DL closes earlier on party nights (either 6:00 pm or 7:00 pm, depending on the day of the party). The first party is likely to be either on Sept 23 or 30, 2016.