Hi Sameer,
do you realize, what your question really is : You are asking "Should I build my own car, using an combustion engine - or should I use a prefabricated car ?
Lets ask it the other way around : What is your estimate to implement this with your own RDBMS system ? Anything above 20 days a thorougly designed, developed, tested, documented, extensible sytem ? Forget it.
With Alfresco, you have everything except the exact metadata model out of the box - Setup incl. servers, backup, firewall adjustments etc. well below a week (5 persondays) for a prod environment, if you have an up to speed IT team.
rg 1) If you cannot work with simple workflows and the advanced workflows, provided as examples, are not enough, you have to develope your own workflow. This is probably by far the biggest workpackage in terms on spent person days
rg 2) The metadata is not "ripped", but property fields of MS office/pdf documents are read. you can automate your own formatimport by adapting a parser. you will, however, have to define content types, which will provide the fields to store the metadata. something you will certainly have to do (much more) with your RDBMS solution.
Norgan