The least, the better. You don’t need too many plugins if your hosting and your themes are good. This list will be kept updated.
The SEO Framework
I’ll be honest here: a SEO plugin is not as important as most websites or companies might pretend. If you want to have a good website, it needs to be light, fast, straight to the point, with excellent content, and with links pointing to it from serious websites. If your theme is good, the technical SEO should be already good enough; otherwise, if it is not, try The SEO Framework, it does what it is supposed to do. Yoast is a good plugin too, but it doesn’t do that much and invade your WordPress with ads.
I am actually making more money with my photos using Copytrack than by selling them. Do you know this service?
Google Fonts for WordPress
I prefer Polylang to WPML. Cleaner plugin, UI and pricing. I had troubles with WPML in the past and even though I proposed fixes and they were accepted, they were never push in new released and bugs are probably still running.