Calculations capacity plan and other

I need to know little about capacity planning for dedicated mysql server with following configuration:
quad-core processors

How many websites I may host - based on what I may calculate this?
What are the limiting factors for mysql - max simulteneous connections, threads, databases? How can I overcome them?

Maybe not even a single website. And you need more memory and more and faster disks.


How good following site is to estimate server capacity based on requirements like simultaneous users, disk space req., server traffic :

No tool will help you until you know what you’re planning for. You need to be able to measure or estimate your data set size, its growth rate and you will need to characterize the expected workload on the database. Once you’ve done that, you can start to capacity plan.

That tool you point out is good estimating the cost of power to the servers, which by itself is pretty useful, but it makes some assumptions about the amount of RAM you will need based on your data set size which simply won’t fit many applications.

That is what my question is all about.
What are those parameter I must understand before deciding.

I read: Setting binary logs to a separate disk other than data directory is better. right?