The interpreter and needed tools are freely available. Its wide use has also led to the development of many tools and modules specifically for CGI programming. No quotas on space. Ability to install, run and maintain CGI scripts. One or more people needs to be committed to maintaining the site, answering incoming mail, developing WWW material, and addressing arising issues.
Email is far easier to handle with little to no CGI support.
In this manner questions and answers can automatically appear on the web. If the option of selecting an OS and WWW server remains, the following points should be kept in mind. OS - The operating system chosen should depend on what's available, internet connectivity, and whether software can be attained at a reasonable cost to carry out all functions. WWW Server - The UNIX httpds offer the most in terms of performance and functionality. Servers cost anywhere from nothing to thousands of dollars.