If I had a single HTML page on a DigitalOcean droplet containing around 500k (filesize) of images, what resources (what size droplet) would I need to cope with over 50k simultaneous views a few times per week?
Would 2GB Memory + 2 CoreProcessor be sufficient?
When a client requests a page from a server, the server closes the communication with the client after doing his work.
Sooo static pages requests do not need loooooot of RAM.
I think 2GB is also more than you really need.
If you can, anyway, maybe it's better to store images on services like Imgur, to save some memory...
Go for a $5 512 or a $10 1GB droplet, install Nginx (there are plenty of guides on DO community guide section, and then use Cloudflare free plan to CDN/Secure/Optimize your site.
You can easily do it with a $5 droplet and no need to host images else where.