I’m a longtime season pass holder and former employee, so I’ll answer what I can. A few easy ones, first, then the loooong part…
Early entry is super hit or miss and I would absolutely not book Breakers just for that! There may be one ride open, there may be 3, there may be none until 30 minutes in 
That said, I don’t think there’s any reason not to stay onsite if you can swing the rates at Breakers. I stayed at Breakers Thursday night last year, then switched to Castaway Bay… we got the free parking for Thursday & Friday, with early entry Friday then left midday to swap hotels. We returned at around 3:30 and found a close spot in the main parking lot (your parking pass from Breakers is still good on check out day) where someone else was leaving. If you have a reservation that’s not pre-paid then definitely check Hotwire as the date gets close… sometimes Breakers will come up as a hot rate, especially Thursday night.
All parking is first come, first served. You can pay more for the closer “preferred” spaces in the main lot, but if you’re arriving early that’s not usually necessary. If staying offsite (including the other CP properties that don’t give you free parking) you can get into the parking lot half an hour before the park opens for early entry. I think that’s sufficient the first weekend in October, especially on a Friday. I took youngest niece and her BFF Sept 28-31 (Thu-Sat) last year and Friday didn’t start to get busy until mid-afternoon, when we were leaving for a midday break. Saturday was worse, but that’s largely because it was a gorgeous weekend.
If staying onsite you don’t park separately… you park at the hotel lot and then walk to either the Magnum or Beach entry gates. The Magnum gate gets a decent line, but it’s not anything close to WDW rd lines. The beach entry is what I prefer (you go to Starbucks, then exit through the back door onto the beach boardwalk and it’s just a little way down the beach to the gate near the Windseeker ride) and there’s not a huge crowd there. Even if there was a bit of a line, it’s not like enough people go in then to make any early entry line get long enough that you won’t be able to ride whatever is open during that time.
I go in right at the start, just because if nothing I want to do is open right then there’s nobody stopping you from moseying on over to Millennium or SteVe and just hanging out there waiting for them to open. I will say that the chances of the new ride being open for early entry in October are 50% or less, even if it’s on the list. Cold isn’t great for coaster speeds, so if it’s cold even if the ride is running great (and it may not be… new rides just have A LOT more downtime) they may not have it open early simply because it’s better to offer something reliable than something that very well might roll back and be down the rest of the hour.
The weather really does play a big role in October, though it only rain/storms or unseasonably warm sunny weather really affect the crowd levels. Cold and wind can make the coasters run a bit slower, and they may not always be able to run all trains or have all seats in the train open if it’s particularly nasty.
If you can get there for Thursday evening park time (6-midnight) then it’s absolutely worth it, because the crowds are a low as you’re going to get… only the bigger rides and haunts are open, but it’s a great way to ride a bunch of those “lesser” coasters with little to no wait at all. Alternately you can knock out a couple of bigs with relatively minimal wait, and do some of the haunts and shows. Until last year it was Fridays that were the 6-12 limited ride, less lines nights, but in recent years that got to be so popular that the lines were just as long, so they pushed everything up by a day and it really helped. If you can do Thursday and rd Friday morning then FLP isn’t really necessary, though if you’re a line princess then you’ll want it for Saturday. I almost never even consider it, but with the new ride this year I’m actually toying with the idea of adding all-season FLP to my pass.
A word on the haunted attractions: they’re not Universal-level in detail, but they’re more… interactive. Read: in your face… they won’t touch you, but sometimes they invade your space for sure, and while they’re often a little cheesy they can be pretty intense. They can and will give chase if you run. There are a few areas that become haunted walk-throughs after dark that take up the entire midway, so if you don’t want to be scared after dark then everyone in the party must have one of the No-Boo necklaces you can buy!
, but it was a wonderful day. Worth every penny.
