Will google ranking or number of indexed pages drop initially??

About to install vbseo fully, but would like some feedback first. Is there a chance that my google ranking will drop, or I'll actually have my number of indexed pages drop temporarily upon switching to vbseo (since my URLs will actually change from what's already indexed on google I guess those pages with the old URL's will drop off google)? This is my biggest fear. Thanks.

Yes, there's a good chance the number of pages will drop because there could currently be duplicate content. vbSEO will help eliminate that.

Depending on elements beyond our control, there is a possibility of getting "sandboxed" by google. I've seen this happen a couple of times now. Of course, vBSEO takes all possible measures to prevent this from happening by 301 (Google's safe way of) redirecting your previous content urls to the new, static urls, pointing the archives to the core content (and) redirecting the previous archive pages as well, etc., etc.

Also, make sure you install & set a daily schedule task for the vBSEO Google/Yahoo Sitemap Generator which seems to be working wonders by enabling SE's to find & index the new, static pages.

Yes, I definitely recommend the Sitemap Generator too. Great compliment to vbSEO!