Hello,

It is always good to scale horizontally - split services out to separate droplets. This means you can “scale faster” by resizing specific components that need it.

There really is not a good way to estimate what size of droplet size you need for it, because there are so many variables. How efficient are your plugins? How efficient is your caching? What are the users doing on your site? And the list goes on....

Nginx and mariadb are a good step towards more efficient wordpress serving. I would definitely suggest moving your database to its own droplet (or a cluster of droplets). If you’re going to use Redis, definitely put it on its own box as well.

W3TC would help out for sure. I’d suggest investigating Varnish as well: http://code.tutsplus.com/tutorials/optimizing-wordpress-with-varnish-and-w3-total-cache–cms-21136

I’d be happy to answer any other questions you might have!

Best Regards,

–Andrew