Docs & field updates

I am trying docs again & can see that we can now enter a bill for purchase receives which is great news !
The docs feature is very expensive if you consider it can cost more than the hosting app, please review the pricing, I'm sure you would attract more users if it wasn't so !

In Inventory I can set up a bill due date as attached image - this is not possible in Books, we are stuck with a set number of days due.
It would be great if this Inventory feature could be incorporated into Books !