Is integrating a unique item selling app with Shopify payment and tracking possible?

[PhilAJ]

Hi - I'm new to Shopify so please be gentle; I'm just after some initial advice.

I have an Application that allows people to Sell and others to Buy specific items, which are registered to people with an App in my system. The actual Sales Pages are within my system, and each item is a 1-off. (Think ebay but only for specific brands). I need to add Payment Processing,  Calculation of Carriage charges; and maybe delivery tracking of goods - which could be worldwide. Hopefully also have some callback to my system when transactions are completed, money paid and item delivered. 

After some initial reading, what I'm hoping to do is;
- Item is marked in my system to appear in Sales Page
- Create an item in Shopify Store - will be a 1-off with no variants
- Show a Shopify 'Buy' button my page in my salespages

- When 'Buy' is selected - let Shopify take over and handle the entry of buyers details, calculation of carriage; acceptance of payments ; tracking of delivery etc .

- Some form of callback - or polling from my site to Shopify - to ascertain status of the transaction
- Update of Assets in my site.

First - is all this possible - and does it sound ok?

Secondly - can anyone point me in the direction of a dummies guide to doing it?

I'm fine with JS, API Calling etc.

Thanks in Advance

Phil

[PhilAJ]

UPDATE: Something key that I forgot to mention - we will be the middle men, and the Products will be supplied from the Seller to the Buyer - NOT from us.
Is it possible to set this up - and still track delivery?

[PhilAJ]

Thanks Olamode_11 very interesting stuff. 
Do you work for Shopify?

I am a Developer so may give it a go myself. If I am only using the Payment and Fulfillment part of the system, does my 'Store' ever need to be seen directly?