No not at all as cases will generally process at differing times.

Yes you may use cash as an asset for I864 purposes.

The last year tax return and corresponding W2 and 1099.

You should answer affirmatively with the legal name of the business.

Yes you may file a second extension request.

Yes you may submit a properly filed application.

They will require separate applications and fee.

It can take a few weeks to months for response from expedite request.

You can use the Avvo search tool to find a reputable attorney.

No you generally do not need to list every client.