Multiple Websites ?

Should a photographer have a website, instagram, facebook, Flickr, (whatever else I am missing) all at the same time? Or just concentrate on ONE avenue?

If you are talking about professionals then the more platforms you are on, that are relevant to your target audience, the more likely they are to see your work. However you have zero real control over social media platforms. They could shut down at any time, taking all your clients with them (or change their algorithm in a way that damages your business).

Your aim for social media should always been to drive clients to your website so that you have a direct connection that won't be lost of a particular third party platform suddenly ceases.