I can share my research - leaving in just over a week. Obviously, I don't know if I will be caught by surprise, but I'm comfortable with my plans.
1) I was told that Acropolis pre-purchase is not needed for this time of year, but I bought a ticket for my preferred date and time none-the-less. You can monitor the sites - check if times are disappearing. I just did a random check for the Acropolis for a day in the first full week of October - all times available. The current availability seems to indicate that pre-purchase is not strictly necessary. If not the case for your preferred day, monitoring the site should indicate this in time to purchase some entry time even if not the first choice. I do not plan to pre-purchase entrance to the Archeology Museum or Agora.
2) Personal choice. I tend to dislike tours. Rick Steves has an audio tour one can download.
3) I decided I was not up to committing to being in queue at 8 AM. I will be visiting a bit later in the AM. I've been monitoring weather forecasts and noting hourly highs. My assessment is that October should be fine at most times of day.
4) I plan Acropolis and Agora on the same day. My research indicated highly walkable. There was a recent post about disruption to the Agora entrance point due to construction. I'll try to find it and link. Access may change before then, but good to be forewarned. The website only indicates to "follow signage" which the forum poster said was not obvious.. Will take it as it comes!
