-How do I find exactly the number of pages indexed by google?
Head on over to google.com and run a search for:
site:www.yoururl.com .
I'd also recommend using their
webmaster tools to set up a sitemap and have access to a variety of information about Googles indexation of your site, as well as handy things such as the most popular search queries that your site is shown for and the position it ranks.
-Does the search engine friendly urls help in increasing them?
It really depends on what you mean by search engine friendly urls. If you currently have
www.sitename.com/randompage.html then changing those to the slightly more friendly
www.sitename.com/random-page.html will have a minimal, almost unnoticable affect on your search engine results, but won't alter the indexing of your site.
If, on the other hand, you have
www.sitename.com/index.php?article=1 or something like that (basically any dynamic pages) then hooking yourself up with some mod_rewrite work to change these to static html pages will help you out, as in a lot of cases the google spider, and spiders of some other search engines, just flip straight past dynamic pages, as they can be used to manipulate the spiders etc.
-I think I am well indexed in yahoo and msn, does switching to se-friendly urls make me lose the pages indexed in them (yahoo and msn)?
Again it depends what is involved in the switch. If your switching from dynamic pages to static html, then as far as I am aware (this is where my knowledge breaks down) it shouldn't change a thing, as you're not amending the actual page location, just the url that sort of masks it. If, however, you're completely changing the page location by turning randompage.html into random-page.html, you'll eventually lose the listings for the former, but hopefully by that time increase the listings for the latter
-Does google syndication help for my case?
If you're referring to submitting a syndicated sitemap to google then yes, it will help - however once again even if a dynamic url is listed in your sitemap, theres a chance it'll get looked over.
Also, please bear in mind that the whole thing with dynamic pages doesn't always happen and isn't always an issue - I recently had a large site with over 44.5k index pages, each and every one of which was a dynamic url