There is no need to feel like you need to get the FOTL before you go. Wait and see the size of the crowds. You can easily purchase a FOTL if you feel you need one when you visit.
Like the PP stated there is no telling what kinds of lines you can expect during October with WWoHP opening soon. Historically there really is no need for the Express Plus pass (there is no such thing as a FOTL pass) and you can always purchase the EP once you arrive...if you find the lines are too long to suit you.
We live in NC and our schools are year round so we always go in October. FOTL is crucial for the newer rides. In 2008 when The Simpson's was a new ride, the wait time for the regular line was 75 minutes. Other rides weren't bad, but we still used FOTL since we were staying onsite. Crucial? Probably not. But with WWoHP opening...I would say it is going to be somewhat busy.
This is what I've experienced too in the last two years in October. Last year we were there the week before Halloween and it was pretty low-level crowds during the day. But with Harry Potter opening up, I think all bets are off.