Can a permanent legal residents of the United States invite a family member to the USA for wedding?

Yes.

Filing Change of Status (I-485) when H1B approval is in pending status.

Yes, you should be able to apply for a DV-based adjustment during the automatic extension period on the H-1B.

Received a intend to Denyl notice when applied for my H1B extension as my masters degree is from a non accredited university.

Your company's attorney should be aware of this issue and understand how to respond.

Is it hard to get a waiver?

Yes. Please consult with an immigration attorney if you require a waiver.

Can an employer pay less than what it says on all documents of an H1B visa process?

No. The employer is violating the LCA.

E2 visa interview

You can expect questions as to the nature and amount of your investment and be prepared to produce any documentation to corroborate your statements.

You must truthfully acknowledge any criminal arrests or citations. Violation of a noise ordinance would not give rise to a ground of inadmissibility.

Selected as the best answer

You are required to answer questions posed to you. Your attorney may interject if such questions are inappropriate, irrelevant or otherwise...

Are there any "salary requirements" for O1A Visa? Extraordinary ability in business?

One of the criterion is evidence that you have commanded a high salary vis a vis others in your field.

You should discuss this with an employment attorney.