JPEGS for event listings, social media posts and email mailings

I need a graphic designer with a VERY GOOD EYE and excellent resources (i.e. access to all fonts and a wide array of royalty-free images) who can perfectly match branding, "look and feel" and layouts for online events marketing. The work entails creating JPEGS for Eventbrite headers, cover art for LinkedIn, Facebook, and JPEGS for social media posts that are congruent with corporate branding and existing "look and feel" of prior event listings. In addition, custom JPEGS and artwork needed regularly for email mailings (Campaign Monitor), etc. FAST, accurate turnaround of work is essential and ability to make changes and take, understand and respond positively to art direction (if necessary). You must understand and have at your finger-tips all of the relevant and accurate sizing/ratio requirements for every eventuality (i.e. different size requirements for Twitter, Instagram, FB, LinkedIn postings versus cover art, etc.) and understand HOW to adjust artwork aesthetically for this without being told. Must speak/read/understand excellent English. The job will be for a fixed term with approximately 5-6 art pieces per month (excluding versions once art is approved). Also, must be able to work and respond at times that are congruent with Pacific Time (US west-coast) to speed up feedback and change orders. Fees offered will be a fixed amount PER MONTH as we are a non-profit with tight budgets.