Hi Max,
It’s not possible currently to set a shipping fee per item, like £6 per key keg, however, we have a feature request for this. If you can give Delivery Charges by product/s a vote, that will help move it up the list and ultimately be implemented sooner.
There’s also not a MOQ feature as such, but there is a minimum order value (MOV) feature, if that could work as an alternative? This can be set up in Settings → Breww Trade Store settings → Customer-based rules. Here you can create a rule for the MOV, and assign the rule to all your customer types (if you’d like it to apply to everyone). If you need MOQ per container type, could you post a feature request for this, and we’ll see if this can be built for you.