As long as he/she wants! However you may create an obstacle to becoming a citizen if you are gone more than 6 months per year. If you have not received a "green card" you will have to obtain "Advance Parole". See website noted in answer 2 and find "forms" for this document. Also see: http://www.uscis.gov/files/nativedocuments/M-480.pdf
for a simple official worksheet of basic requirements for citizenship.
A Conditional Permanent Resident is issued a card valid for two years. In order to remain a Permanent Resident, you must file a petition to remove the condition during the 90 days before the card expires. The condition must be removed or you lose your permanent resident status The card is valid for readmission to the United States if the trip was not greater than one year in length. If a trip will last longer than one year, a reentry permit is needed. see site: http://www.uscis.gov/portal/site/uscis
seven weeks
well, it depends what status you are living under. Like a permanent resident or on a visa. If you are a permanent resident then you can stay here as long as you stay out of trouble and renew your card when it expires. If you are using a visa, then you have to leave when your visa expires or apply for an extension.
no
If you are a conditional resident 90 days before it expires you need to adjust status and get the green card with 10 years validity. Permanent lawful resident can stay as long as they want provided they renew their green card which is valid only for 10 years.
3 years of being permenent resident then you can apply
s he will have to stay, or he may run of , and the divorce case becomes complicated and delayed as well.
No , as long you are not earning income from it and are already a permanent resident and not in the progress or application.
As the Nigerian requires a visa to enter the US, he /she can stay as long as the visa is valid. If the nigerian has a green card, then he/she can live in the US for any period of time as it gives them the permanent resident status.
no, only us citizen can help for permanent resident
Yes, but it will require the person to return to/wait inCanada for a spousal visa to become available. That should take about 2 1/2 years when married to a permanent resident. When marrying a permanent resident, you CANNOT stay inside the US while waiting for a spouse visa/green card during that time.
yes
Deportation is possible. depending on how long you have been in the US.