Graph fulfilment, vendor orders query

[jonmjones]

hi all, 

I'm looking to make ordering inventory a bit simpler for the admins and wondering if theres something already baked in to Shopify's extensive graph api. I can see fulfilment orders and inventory movements, but don't quite understand it all.  

I'll explain our scenario.

• We order on demand from our warehouses for shipping direct to purchaser or to our bricks & mortar store for collection. So order placed by purchaser, then line items are ordered from various locations and sometimes manufactured to order (e.g. embroidery) 
• We don't currently have a way to record what has been ordered for which line item, and just rely on the manual ordering process to ensure items are delivered.
• When ordered, the mark as fulfilled button is pressed
• Tracking info is subsequently added as and when we get it from each warehouse/factory.
• We allow collections of part orders, but currently have to keep a manual record as the Shopify Order page does not allow part collection.
• We'd like to some how store what was ordered from which warehouse and when it is shipped/collected on a line item basis

I don't want to plug in some random app that might (but probably wont) meet our needs for $$$ per month and would rather develop something ourselves, hence me reaching out for advice on the graph apis to use (if they even exist)

Thanks in advance.