Do I need to have some kind of income so my boyfriend can apply for his residency?

Your boyfriend cannot apply for a residency on the basis of his relationship with you unless all of the following conditions are satisfied: a) you are a U.S. citizen; b) he and you marry; c) you file an immigrant petition for him, and an affidavit of support showing that your income is no less than the federal poverty guideline (for this year - $15130 for a family of 2, $19090 for a family of 3, $23050 - for 4, etc.); if you do not have enough income, you will need someone else, who does earn enough, to file a second affidavit of support as a co-sponsor; *and* d) your boyfriend entered the United States legally, or he is in the U.S. since before December 20, 2000, and a relative or an employer filed an immigrant petition for him on or before April 30, 2001 (or, if he was a child then, the petition could have been filed for his parent). If you are not a U.S. citizen but have a green card, the requirements are even more difficult. In any case, I recommend consulting an immigration attorney: rules are complicated, and attempts to prepare the papers on your own are likely to result in denial of the application (in which case your intended husband would face a very real prospect of deportation).

Yes if you are petitioning him as a finance or spouse.

You will want to consult with an attorney with your boyfriend to discuss his options and what requirements would be associated with any options he may have.

Yes, you have to be a sponsor for affidavit of support purposes. The amount of needed income depends on the size of your household. If you do not have sufficient income, you can get a joint sponsor to sign the affidavit of support on his behalf.

Yes, you will need to be married, and as the petitioning spouse, will need to meet the minimum income requirements of the I-864 for your family size as noted on the I-864P. Please note that your (then) husband will need to qualify for the permanent residence as well, typically based on his current U.S. immigration status or other possible grounds of inadmissibility.