ON the cover letter question, I think a cover letter should *always* accompany a direct application (i.e. not through an agency) and should address any selection criteria mentioned in the advertisement.
If they ask for “3 years XYZ experience” the cover letter is a great place to confirm “I have more than three years XYZ experience, including blah-di-blah” or even “While I have only been using XYZ for the past 12 months, my 5 years experience of ABC will help me become productive in a short time”
One sentence (or so) on each requirement will help the recruiter without them having to scan your whole resume to search for the relevant parts.
When I am recruiting, the resumes are the second document I read — and a poor or missing cover letter means your chances of me bothering to read your resume has fallen.
It’s a shame, but if I have 50 applications for one role, then taking even 5 minutes to read each one is 1/2 day gone. That cover letter is your opportunity to get noticed.