Yes, you need to purchase an extra ticket for this event.
The tickets sell out very fast.
You can be in the park that day if you want to use your regular admission ticket, but most wait till the start of the celebration, which is around 4:00 p.m.
The park usually stays open till 1:00 a.m.
There is a special Halloween parade, places to trick-or-treat and get candy, but I heard in the last couple of years, the candy has been so-so.
The event is held at the Magic Kingdom.
I in no way would discourage anyone from going-
like you said-you can have fun no matter where you go.
But,
Universal Studios is a little more for "older" people, ie., teens, people your age. I think theirs is called Fright Fest-you may want to google or look at the Universal Board and see if you can find any topics.
If you do go to the
Mnsshp, do dress up. Everyone does. At least get some Halloween t-shirts. You will be amazed at the people in costumes.