Sharepoint Foundation requirements

Hi,

I want to use sharepoint foundation 2013 for my business use. I've few questions related to that -

1- What other licenses (for example Windows Server, SQL server etc) I need to use sharepoint foundation.

2 - What are the limitations using sharepoint foundation.

3 - Is there any time limitation using sharepoint foundation (how long I can use sharepoint foundation).

4 - How can I provide access to my clients & external users?

5 - Any other specific point to be considered....

Thanks in Advance...