Such questions are impossible to answer on the basis that all websites are different.
Let's consider two different types of website:
- A HTML/CSS website which is 200 KB in size.
- A WordPress PHP powered website which is 2 MB in size.
The WordPress website is going to require a lot more resources (CPU power, Bandwidth, etc) than one of the HTML/CSS website.
Even if we know the type of website, there are still too many potential variables that impact how many visitors an account/server will be able to handle.
As a general rule, make sure to cache as much content as possible, which will reduce the amount of resources required to serve the content. You can also off-load assets to third-parties. For example, instead of hosting large images locally, consider using a specialist service such as Imgur or Google Drive.
