Congratulations on the start of your MBA journey! At first blush, it appears that you have many of the qualifications that OxBridge seeks - international perspective/global lens, 700+ GMAT, good undergrad credentials (though the caliber/ranking of the school does matter and you don't provide that here), proof of promotability over your 4 years of work experience. Solid stuff!
To answer some of your questions about your job offer, you won't be too old if you wait another year or two for OxBridge, unlike top 10 schools in the U.S. which optimize slightly fewer years of work experience. If you want to take the job offer at the biomedical company to burnish your resume a little bit, it might make sense to wait a year to apply but given all the uncertainty w coronavirus it might be better to apply now to get a plan in place. If you plan on applying this fall to enroll the following year, switching jobs now might look a little strange but you can certainly work with it (especially if you couch your reasoning in the fact that you'll be there for over a year before school starts so it will be a great year of experience that you can bring to the MBA). Regarding comp, schools do care somewhat about comp in the sense that they want people who are highly employable and who will command good salaries from recruiters and pick their averages up (average comp and % employed shortly after graduation are very important metrics for school ranking). One proxy for salary post-MBA is salary pre-MBA - though that's a messy and fraught and not always accurate proxy, there is some truth to it.
As a journalist, you will be a non-traditional applicant, so it will be really important for you to demonstrate that you *already* have skills that are useful to employers. If you take the media manager job with the biomedical company (and maybe even secure a promotion or raise while you are there), then you can potentially make the case for a more multi-faceted and business-credentialed application. Given your super competitive demo, you'll also want to make sure that you are differentiating yourself with regard to extracurriculars and non-work leadership (e.g., community involvement, non-profit board or membership participation, civic engagement, volunteering, music hobbies/passion, etc.).
You'll also want strategic positioning that is differentiated from your demo in terms of the impact you want to achieve *POST-MBA* (both immediately after school and long term) and you'll need that to sync with your prior success so that your ambitious goals seem plausible attainable. Your skill set as a journalist will already be rarefied among applicants to B-school, so you might consider positioning your post-MBA dreams in a way that leverages those skills (Some ideas that are worth throwing out to illustrate how you can weave the common thread -- strategy communications at XYZ company, leadership development program at publishing house, Media & Telecom investment banking, equity research covering media companies, LA-based general management program at entertainment company, etc.). Just make sure to do your networking and research to make sure that the things you express interest in doing have been done before by other graduates so that there is plausible precedent for your goals (again, they want you to be imminently employable).