Releasing a CMS under the GPL?

I have created a custom CMS system that I am beginning to use for my clients. I like the idea of open source software and I am thinking about releasing it under the GPL. The CMS does make use of 3 other open source scripts, FCKEditor (GPL, LPGL or MPL), XTemplate (LGPL and BSD) and Magpie RSS reader (GPL).

What are my options? Is the CMS required to have a GPL license, because it uses those other open source scripts? Would I gain anything by distributing the CMS as a GPL script or would I be better off (in a business sense) keeping the code to myself and using it for my clients only?

Thanks!