I just wanted to clarify this, if you want to go into the parks earlier in the day you will need either a single park admission or park hopper. BUT once ToT starts you only need the ToT ticket, that covers your admission into the DCA, you do not need anything else. All after hours special events include entrance into the park (only one's were the park is open to general admission do you usually have to buy seperate admission).
I also would say do not worry about getting your tickets all that early. Like I said we bought ours days before because of some confusion and had no issues getting tickets. This event does not sell out months before, I would only worry if you were trying to buy same day tickets or Halloween tickets a few weeks before the holiday. You will be fine
ETA: They also completely close DCA several hours before ToT to set everything up, so even if you have a admission ticket and plan on going to ToT you will have to leave the park and the re-enter when they re-open. Which is very different then the event at WDW I know.