Your question raises some serious concerns. Please contact an immigration attorney for private advice. Thank you!

Benefit on U-Visa?

U visa category is not affected by the public charge issue.

Some H4 foreign nationals can seek lawful employment authorization. You should consider that option and should seek a private consult.

Can a file for citizenship after 3 years of being a permanent resident under VAWA?

You could benefit from private legal advice.

A dependent spouse J or H1 could study. You could also benefit from legal advice.

Answer the best to your understanding. If you feel more comfortable answering each position separately you could do so.

Can I change my visa status from H4 to the visitor visa B1\B2?

You can file to change status now. Check form I-539 instructions if self filing.

For affiditit sponsoring, my wife is a student and unemployed. Will my income in U.S and savings be enough for I-864?

Your post has insufficient information. Please seek private advice, you can benefit from it.

Can I change the return date after applying B2 ViSA extension?

Yes, it is a good idea to apply for an extension.

I-485 and I-290b?

The agency has its process and file is moved from one office to another. It is best to provide the entire file to an attorney and discuss whether...