Entry level positions tend not to need them. I would say the only time you would need or want a cover letter is if you have extensive experience in a set field or you are applying for a creative arts position.
I don't think you do, not these days. A friend of mine often sees a lot of resumes and he tells me that most people don't even bother with them. Having a single sheet with everything on it is best.
I don’t think this is a thing people look for these days. Most resumes I have seen don’t have them no mention using them. You can always make one and use it if you think you need it or if it is required.
Better to be safe than sorry and use a cover letter in your resume. Worst case scenario, it just gets looked over but if they are expecting one, it could cost you a job opportunity.
I was always under the impression that a cover letter was only necessary when the job required you to bring in a resume in person. I could be wrong though.