1. That's optional. Include it if it helps keep your mind at ease regarding your case.
2. Include copies of all.
3. The response to this isn't a simple yes or no. Usually, I'll encourage petitioners to provide as much documents as they possibly can with their submitted petition. For instance, if your FO happens to be one where they approve DV based AOS cases without an interview, including an affidavit of support in the case of someone who might be considered a public charge makes it easier to get one's case approved without the FO having to make an exception of asking the petitioner to show up for an interview. And in the case of where an interview is normally required, having a 'complete' package enables the IO to fully review the documents prior to the petitioner showing up for their interview. However, does it make sense to delay the package submission on the basis of still waiting or looking for a sponsor? No, I wouldn't advocate that.