It needs to be in your account 2 months prior to applying. So if you apply say 20 days early on the 20th September then the funds must be in the account by 20th July. The fact that your extension is due 10th of October is irrelevant. It’s 2 months prior to applying.
There isn’t a set amount of times you can get a non O during a one year period. The embassy you are applying through will decide whether to issue you one or not.
You’d probably not have an issue trying for two. Perhaps an issue if more.
If you manage to get the visa I really can’t see you having any form of issue with immigration even with a history of previous entries as you have a valid long term visa to enter. That’s not a given as though it’s up to the individual immigration officer.
While some people have attempted this, it's not advisable as your application may be denied if you're not in the country where you applied. You might also be required to attend an interview at an embassy or consulate.
I’m assuming you have an extension of stay stamp in your passport. If so you’d need to get a re-entry permit from immigration in order to keep that stamp “alive” for when you return.
You can get one at your local immigration office or at the airport just before you fly.
On your return you’ll be given a stamp that matches your current “allows to stay until” stamp.
Also you’d need to do the TDAC prior to your arrival. It allows for up to 3 days prior.
When your visa expires is irrelevant. You used it to get in to Thailand and as it’s a Non B single entry it is now finished.
What matters is the “allowed to stay until” stamp you got. If that’s what you are referring to when you say 4th November then that’s when you can stay until, regardless that you are no longer working.
If you had an “extension of stay” stamp that you got from a local immigration office then when the reason for the extension stops so does your ability to stay unless you switch to any other type of stamp. From what you wrote I’m guessing this isn’t the case.