This would be quite specific on the website and the plugins that you have.
If you are getting 100,000 visits per month, this is around 2.5 visits per minute, this could be handled with a fairly small well-optimized server.
What I usually suggest is the following:
- Make sure that you’ve optimized your website as much as possible by removing all of the unnecessary plugins and installing a good caching plugin.
- Tweak your server configuration for maximum reliability and performance.
Then after that make sure to run some stress tests for your website to see how many concurrent connections it is able to handle. In the meantime monitor your server performance and tweak the necessary settings. After looking at the results you will be able to identify if you would need more resources or not.
For more information on how to get started with load testing you could take a look at the following tutorial:
Finally, once your website goes live, make sure to use a CDN like Cloudflare.
Hope that this helps.
In this article, we'll talk about the server side of web performance optimization: how fast can your server respond to your user's requests? We'll review the general landscape of load testing, step through a plan to find your server's maximum practical response rate, and discuss some options for open source load testing software.