Concrete5 opens a database connection at the first part of the request that requires a database connection and this connection persists through the rest of the request at which point the connection should be released.

Most likely you're never going to hit this 50 active MySQL connetions at any given time because the hosting provider isn't going to let you run 50 concurrent requests at any given time. According to a WHT thread I found it looks like they limit you to 15 php processes running at any given time so that's going to be your bottleneck (assuming you don't hit CPU or disk contention before that).

Ultimately, if your client is actually going to have a high traffic website, you need to look into something other than shared hosting because you WILL have resource contention problems.

That said every person has their own opinion of what "high traffic" is and sometimes you just have to try it to find out if something is going to fit their needs or not.

To answer your question though, typically each request uses 1 connection to the MySQL database.