Yes it can make a difference in terms of strength and organization of case.

No you would not qualify if separated.

Yes he should be able to despite visa overstay.

It can still take many months until a visa interview is scheduled.

Not based on friendship alone but instead through family or employment based means.

A cosignor will be required if your spouses income is not sufficient or there is no documentation of this.

She will need a returning resident visa or SB1 visa. Consult with an attorney for guidance.

They can apply for a tourist visa through filing form DS160.

Write to the USCIS service center and advise of departure/withdrawal.

Contact USCIS to inquire about status and whether RFE for medical has been issued.