I plan to use CMF but want to avoid using Topics. ( I already have more than 3,000 products being sold using that PHP shopping cart. Need as light an approach as possible. )

While it's said that the default topics are a bit pokey, it's not a necessary feature, and some new implementations are a lot better. Topics are really meant for stuff like this. If you're going to use CMF, you might take a look at CMFCommerce at the Collective on SourceForge. It's on my list of things to install, but, well, it's still on my list. --jcc