grammar - Comma before "with," "who," "having" for non-compound sentences

Your use of commas is fine in the five numbered examples you presented, and your career counselor offered you confusing advice about punctuation (even though she may be outstanding at career counseling in general).

In terms of substance, excellent computer skills involve a lot more than typing speed, which is a relatively small part of computer literacy. Far more important is your familiarity with Microsoft Office programs, including Word and Excel, and especially any proprietary or specialized software specific to the industry in which you seek employment.

Speaking strictly for myself, as an employer I am put off by an applicant who thinks it is important to mention his or her typing speed in a cover letter. There are exceptions, of course. If it has been your life-long dream to become a medical transcriptionist, for instance, then it would be very important to highlight that ability, along with an outstanding medical vocabulary, excellent editing skills, and exceptionally good comprehension of spoken English. Otherwise, it just sounds like you are bragging. Please keep in mind that the person who reviews your application probably types at 40 wpm or less. As a Stanford graduate, you hopefully will not spend eight or more hours a day speed-keyboarding, which is extremely tedious and stressful work.

If you want to keep it in, then I would recommend, "I have excellent computer skills and a typing speed of 80 WPM. I'm fluent in [...] Microsoft Word and Excel, as well as [...] Adobe Photoshop and other imaging software" (or CAD/CAM applications, GIS software, or other specialized programs in math, physics, design, layout or whatever else may be required for the job). Under no circumstances should you write, "and therefore I deserve..." anything! An entire generation of students raised with the fantasy that everyone should have high self-esteem (rather than "accurate self-knowledge") has created a false sense of entitlement that clashes with the reality of working in the real world.

The key is always to write for your reader, not for yourself. Put yourself in the employer's position, and ask yourself what you would want a highly qualified applicant to say about herself in her cover letter. Try to avoid cliches and be honest and direct about your experience, education and accomplishments. You'll find that it results in far more positive responses from your prospective employers.

Good luck, and don't worry about your use of commas. You've got it!