How long do you have if your living oversees to get to the US once the visa is issued? i.e. how many months can you stay oversees before you have to depart for the US?

Another question I have is if you are working oversees, can your income count for the I-864? I am planning on living overseas with my spouse for a little bit and do not know if the income will be enough, so more than likely I will need a co-sponsor.

Another question... Can I use my parents address as domicile?

an immigrant visa is usually valid for a maximum of 6 months from the date of issuance. you must travel to the us within that 6 month period or else you have to start the process over.
JK

6 months

Six months is correct.

You cannot use overseas income unless it will continue when you return to the US. If you won't be in your spouse's country for long, you probably won't have a domicile issue. As long as you continue filing tax returns and keep American accounts open, your parents address should be fine. It can vary between different consulates though so I would check with someone who went through the same consulate.