Customize Spree Checkout

Hi I am wanting to use spree in a specific way. I am looking to use Spree as my backend shopping cart only. Which means I want to be able to make front pages using any other tool available out there like wordpress but I want the sales to goto my Spree Backend so I can manage them easily. In short user will be shown pages build in wordpress and will be directed to the checkout page I created in Spree. Also on checkout page somethings like order bump and select product quantity needs to be configured. It should be achievable by using Spree API calls. Let me try an explain this with an example. Say I have added 4 products on spree backend. Now one will be used on main landing page and 2nd will be used as an order bump. 3rd and 4th will be used as one click upsell. For those who do not understand the terminology. Order bump is simply a product that can be added to your cart simply by checking a checkbox underneath your add to cart button. Lets' say user have decided to buy the product 1 with or without the order bump. (This means at this point user have entered his credit card and hit the order now button). Once that is done user will be shown product 3 as an upsell and will be asked if he would like to add this product to his order as well or not. (Any number of upsells can be presented to user.) Once Order is placed it should be submitted to my spree backend. I am looking for a seamless integration of this all with my pages or any future pages I will be making. Apply to this job if you can do this or if you need to clarify anything. Please do not apply to this job if you are neck deep in work and ask me 1 or 2 months to do this job. I need this done in one week time. Thanks!