Are new hire classes starting in Oct and how many a month are they doing?

Airbus side: 4 new hire classes of 10 each in Oct.
2 new hire classes of 10 each for Nov and Dec

Both the November classes are all airbus?

Yes, two classes in November. I'm sure there are Boeing new hire classes as well.

When is the soonest you’re able to change aircraft?

As soon as a new bid comes out, you’ll be able to bid into a different aircraft/base. You’re not seat-locked as a new hire. Only after you switch aircraft do you become seat-locked for 2 years.

We all know what you meant by seat lock, but just to remove doubt for anyone not on the property - you’re locked into that position and equipment for two years, unless you’re awarded an upgrade.
Example: You could be Airbus as a new hire, spend 4 years right seat there then bid Boeing FO, finish training and incur a 2-year “seat lock”, but then get awarded Airbus CA on the next bid. You could not get awarded Airbus FO.
Example2: You get Airbus FO as a new higher, then 6 months later bid for Boeing FO. After Boeing training you would have the 2-yr equipment/seat lock.

The latest huge bid closes before the first newhire class in October. Considering this bid is effective May 1 and takes care of summer staffing, a logical conclusion would be the next bid effective date would be around ~September. Effectively, newhires right now should plan on being on their plane until next Fall.

Tentatively, the next bid should be out in June with a November 1 effective. Similar size to the last one with 36 CA and 36 FO A320 reductions.

Back in the prediction game again? That's ballsy after your latest round.