I've been playing around with Hyperledger Composer, following the excellent tutorials at https://hyperledger.github.io/composer/tutorials/tutorials.html
I've come as far as to generate a REST API to my running business network.
as you rightly point out - the Hyperledger Composer Developer tutorial takes you through a very simple Commodity Trading business network (highlighting the acceleration aspects of developing blockchain apps and blockchain 'smart contract' logic using Composer, gaining an understanding of its modeling capabilities and its powerful toolset).
In simple terms, think of Hyperledger Fabric as the blockchain infrastructure (where you see blocks (of transactions) - eg such as shown on the Explorer UI you mention) and think of Hyperledger Composer as a layer or level of abstraction above Fabric (but ultimately uses Fabric as the blockchain network). Quick overview here should make it clearer - Youtube https://www.youtube.com/watch?v=kI30R9iIUWs
So for your PoC (to showcase your business network), you can do the following:
Its really that straightforward. Hyperledger Composer takes care of the consistency (data types, formats, relationships between records eg owners of an asset, how to model then interact with your data on the blockchain) and lets you get on with driving your PoC (and what you want to convey) - or going forward, building your use cases using Composer !
My advice is to complete the end-to-end Developer tutorial, become familiar with everything in that and understand what you can achieve. They try the Queries tutorial to see the power of queries too. From there, you should have some very good insights for your PoC.
Hope this helps.