Custom SEF - SEO For Jom Social - Joomla - 40,000 mebers

we have a site ----------------------------- Joomla site ----------------------------- we need a seo specialist - we have joomla site with jom social - which has now been modified (user membership and stuff) - we need you to SEO and SEF each profile now want is string SEO - to bring each profile into Google... so string Keywords , Descriptions and Tags - for all 40,000 users we do want short urls but theres a problem when we use sh404sef teh URLS are generated but they slow down the site 40,000 users and theres x2 to x10 duplicates of some... that BIG numbers so what we wants is teh short url to still work but do not sue sh404sef but maybe another safe way?? - NO duplicates and NO Server Slow Downs please note we cannot have any of our existing URLS edited on our site or SEF on any other stuff.. This is only for Jom Social!! Thank you - explain to us what you will do, thank you