I need some new modules and feature for my site

Dear Everyone,
I had a custom application Website ( CodeIgniter )
The site is working smilimar with groupon and it created for restaurant. i would like to make it change about the car ( like user can post listing for unwated car and collector can offer for the prices )

The system of stie now charging % of each purchase, know i would like change the way of charge that will be charge for post unwanted listing for example
Free for a 7 days
£10 for 20 days
£20 for 45 days as the day will show on time left.
£5 Feature listing
£5 Highlight Color to stand out deal.

Now i would like to make some new module and feature.
1. I would like to have some new desgin related with car ( clean and look professional )
2. The user can post deal about unwated car here some information ( Frist name, Last name, phone number , email is option) and information about Vehicle as ( Vehicle make/ Model, Registration number , Registration Year )
3. buy now that user can put price that they want to sell that unwanted car , and under they have a box call offer that box will be for collector if they think prices too high, they can offer prices under prices of buy now. ( we dont accept any payment or charge from buy now or offer prices we are only accept for post listing )

How it works
4. have address and calendar ( that show time and date when vistor can stay to wait for them collect the unwated car )

When collector click buy now they will email for vistor of car to let they know that someone interested your car.

After that the listing will be hold as information like Waiting for Collector. After working with seller and collector outside of car as they come their address pick car pay cash and seller confirm as deal off. If something happened or they not happy talk. the seller as relisting without any charge.

The payment gate need to integration with paypal as website payment pro that accept credit process and normall with collector use paypal account or not.

Here all information i got in my mind now. During of project if i need add more or change something i will let you know or you can suggest for me any good information
Thanks
LEO