What is the best way to define connection string for a web application that has minimum 500 live users on the internet in terms of connection pooling. And load factors to consider?

Suppose I have connection string as follows:

initial catalog=Northwind; Min Pool Size=20;Max Pool Size=500; data source=localhost; Connection Timeout=30; Integrated security=sspi"

as Max Pool Size is 500 and as live users exceed 500 say 520 will the remaining 20 users experience slower page load??

Or what if I have connection string as follows which doesn't talks anything about pooling or Connection time out? How the application behaves then?

initial catalog=Northwind; data source=localhost; Integrated security=sspi"

I'm using "Using statements" however to access the MYSQL database.