Build a Website -- 2

Hi I already have website installed using drupal. I need help to develop additional pages in php. complete details below: 1. Website is for selling / buying cars or bikes online. 2. Need additional coding in php and drupal to add a component "sell your car now". The user should be able to login with his car/bike registration number as his / her userid. [only registration numbers should be used as userids]. this should integrate with the existing website which is already online. 3. user who posts their AD online should be able to pay a minimum premium value and checkout successfully. 3. Add a login / signup link to the front end. [module already exists, only should add this feature to the front end] 4. If any user likes a vehicle, he /she should be able to contact the advertiser from the website.