How is the demand for working in media organizations (journalism, talent agencies, social media engagement) in general in Japan, and language?
Don't know, but I suspect mediocre at best. Do you have a degree related to these fields? Experience? Plan on most jobs needing Japanese ability.
What is expected of the proficiency in both Japanese and English, besides the N2 as the minimum for most other jobs in the country?
JLPT 2 or better in the vast majority of cases, as you stated, is the official thing you can get a number to show. Otherwise, just expect to be able to read, write, and converse at a high level. Businesses use email in Japanese, and most companies/institutions use spoken language in Japanese. That means being at least proficient in a modicum of politeness, if not being well-versed in keigo, too.
You know, pretty much the equivalent to your home language being required for jobs in your home country.