When do I file the DS-160?

You must wait until the I129F is approved and you are prompted to do so once the case is with the NVC. See DOS site here where the National Visa...

Will my income of $39,500 a year before taxes be adequate for a family of three, two of whom will immigrate here next year?

Refer to the USCIS poverty guidelines for specific amounts here: https://www.uscis.gov/system/files_force/files/form/i-864p.pdf?download=1 It...

Will my credit card debt or any debt for the I-129F beneficiary, my fiancee, have any bearing on our application?

No your shared debt should not have a negative impact on your fiancé petition - if anything it would add to proof of the good faith relationship...

How?

Yes she does need to prove domicile for sponsorship including proof of residence, employment, family ties, etc. Refer to USCIS instructions for...

What?

As a USC or LPR your cousin can act as a cosponsor and will need to complete Form I864 along with your mother.

Would an arrest affect me getting an immigrant visa?

This should not impact your ability to obtain an immigrant visa but you need to acquire a certified criminal docket with final disposition of the...

How can I correct a mistake on my day-260 form?

You can amend the form at the time of interview, otherwise you would need to complete a new DS260, which for this minor change is not advisable.

How can I bring my family from russia to here? I applied asylum in USA:

It is not advisable for your wife to go to Guam to apply for asylum. Consult with an attorney in private for further guidance.

Apply for FOIA any negative effect? I140

There are no adverse consequences to applying for a FOIA however your employer would need to do so in your particular case re: obtaining a I140.

This should not impact a consideration of your good moral character but it is still advisable to consult with an attorney with more information...