Integrate same category/subcategory urls for WP posts & non-WP CMS pages?

Hi everyone!

I have a portal site with many categories and subcategories (custom non-wordpress CMS in PHP). Im adding articles powered by wordpress. However as this site is a portal site I want the folders/categories and subfolders/subcategories to rank high in google so I would prefer relevant articles to be in the same category/subcategory path as our other content, rather than in a different blog folder. (a blog folder at the end of the path is ok though)

My site root and each folder/category already have home pages. They are mainly non-WP content but I would insert matching wordpress posts for that category (easy part)
e.g. Mysite.com/travel
mysite.com/insurance
mysite.com/insurance/car-insurance
mysite.com/travel-insurance

I want mysite.com/insurance/car-insurance to rank high for “car insurance” so I presume it would be best if all the car insurance articles were on that URL like mysite.com/insurance/car-insurance/article-title, rather than mysite.com/blog/ (correct me if I am wrong?). Plus some categories I may set up on their own domain if http://www.bestcarinsurance.com -> hosted in the folder mysite.com/insurance/car-insurance/ then car insurance articles shd be in that folder too, not mysite.com/blog, right? Mysite.com/insurance/car-insurance/blog is ok though!

Maybe it is possible to install wordpress in the root concurrently with my existing CMS. But then mysite.com/insurance would go to a wordpress page listing wordpress articles. I want it to go to my non-WP content page for insurance. Every main category or subcategory url shd go to my non-WP content page with a box of relevant wordpress articles, not the wordpress navigation page, that can be moved to a blog folder at the end of that category url.
Mysite.com – our non-WP content page (has box pulling articles)
mysite.com/blog – can be a wordpress page navigating all articles
mysite.com/insurance – our non-WP content page for insurance (box pulling articles in insurance and subcategories like car-insurance)
mysite.com/insurance/blog – can be wordpress page with insurance articles all articles in insurance and subcategories like car-insurance)
mysite.com/insurance/car-insurance – our non-WP content page for car-insurance (has box showing articles in car-insurance). Etc. (note we don’t even really need the dedicated /blog/ pages, can really just paste a box onto our non-WP content index pages).

What if I do this? http://codex.wordpress.org/Giving_WordPress_Its_Own_Directory
Then can mysite.com go to my non-wordpress content home page? And mysite.com/insurance/ go to my non-wordpress insurance home page?
Can I install the blog at mysite.com/blog then set the permalinks so they are mysite.com/insurance/car-insurance/ to match in with the rest of our sites content (NOT mysite.com/blog/insurance/car-insurance/

Or what if I install separate blogs in each category folder and power them all with wordpress MU /wordpress 3.0? However if one blog is mysite.com/insurance/blog if I put the car-insurance posts there that is still not as good as having them within mysite.com/insurance/car-insurance folder right? So could install a wordpress in all the final path folders, but then if browsing a higher category like insurance, to display the subcategory articles would mean pulling from different blogs? Also I need a total RSS feed and RSS feeds from every category to power my email newsletters, facebook, twitter etc.

Or maybe I shd install our non-WP CMS and wordpress both in root and would it work with some moving of index files and changing of .htaccess files etc?

My site has about 15 categories like mysite.com/insurance and each of those usually has a few subcategories like mysite.com/insurance/car-insurance and mysite.com/insurance/travel-insurance/

If you think best to do it different, please let me know – given this is a portal site with many categories and subcategories, what is the best way to add articles?

Thanks so much guys! would really appreciate any help, have tried everything and everywhere but no luck so far!