How should I answer this graphic design job opening email?

I received a job opening email from a company that found my resume on indeed.com.
It is a job opening as a graphic designer.
I replied back immediately to tell them that I am delighted and interested.
They replied back with a email saying:

Hi, J******,

Thank you for your response. We are looking for a designer with a strong eye for marketing communications as well. The position would be supporting about 5 different handbag lines; responsibilities include hangtag/packaging design, digital look books, evite graphics, photo re-touching, online/social media marketing materials.
Is this something you'd be interested in? Also, what are your salary requirements?

Thanks,
E**********

My question is, should I reply back with a brief cover letter respond? since the cover letter wasn't involved because they found my resume on indeed. Or should I briefly tell them I am interested and believe my experience will qualify for the job?
For salary, I am planning to state my desired number and mention it's negotiable.
Thank you in advance for answering this question.

Everything that would be included in a cover letter is already known to them and they seem comfortable communicating via email. I would reply as you described and make sure to include a note saying something like, "If more information is needed please let me know."