If speed of access is important then 1 click access can only be offered by full list of topics on the main site, 2 clicks if its hidden.
Alternatively a tag cloud might be better than categories, as I myself can never put 1 thing into a single category.
To not to confuse first time visitor a few major topics could be offered at the top “What is Fusion, Fusion Technologies, Who We are(What we do), Impact (Speculation)”