Help Building a Website That gives Points to Users for Completing Offers

I am in the planning phase of creating a website which will give users points/rewards for completing offers. For this I would need a offer wall type of feature and other features like user login, ip tracking, paypal integration, etc. Which platform should I use? Is there a wordpress theme which gives the same features or do I have to go for something else?

Help will be highly appreciated.

I suggest you Wordpress or make it in PHP(Zend framework) will be great to make it done.
Any more help let me know