In this case I do not think the first step is to rewrite a client but to define a good default settings/setup for such business. Once you have a system working correctly, you can clean the UI from unneeded stuffs (if there are).
I’m pretty sure that the difficulties do not come from the UI but from the on boarding.
I have already created some vertical application in Tryton and by having good defaults and clean UI, I could get (almost) untrained user to work on it.
For me the main point to improve is the blank state of the client: Blank state improvements