Submitting child sitemaps too alongwith sitemap index file ?

We have a rather large site, with 100 million plus records in DB

I’ve created sitemap index file with child sitemaps that confirm to the sitemaps.org protocol.

All the child sitemaps are uploaded to the server and I have submitted the sitemap index file to Google via Google Webmaster Central ( GWC ) account.

My questions are:

1)
In addition to submitting the sitemap index file to Google Webmaster Central, do I need to submit the child site maps too individually?

2)
We have mod rewrite in place and all url’s are search engine friendly along with unique title tags.

Link building activity is underway to increase the link juice at root as well as category level pages.

Is there anything else that can be done to get the maximum number of pages crawled & indexed ?

Any guidance would be highly appreciated. TIA.
-AD