I want to check whether any SDL Web 8 CME website related information (like host headers, port information etc.) is stored in any table in Tridion_CM database. When I try to install, I am getting an error mentioning the Host Header combination for the new website already exists.
This error you receive during the installation is most likely because in IIS, you have already a website configured running on the port or host header you specify during the install.
The solution is either to stop/delete any of the websites already defined in IIS (provided they are not used right now), or specify a different port or host header in the SDL web installation wizard.
You can find more information about bindings in IIS here : https://blogs.technet.microsoft.com/chrad/2010/01/24/understanding-iis-bindings-websites-virtual-directories-and-lastly-application-pools/