Attkey wrote a plugin a few months back for a client that on the save of a work order would check the input items and see that there was enough stock of each, whilst this didn't deal with sub assemblies as the client didn't use sub assemblies I don't believe it would be that hard to modify it look through the sub assemblies also given that the structure should be the same i.e. a sub assembly has stages and input items etc.
I would also suggest that one of our consultants could provide some online training (either Goto Meeting or Zoom) on the manufacturing section of Jiwa, normally I would suggest that this could be done face to face given we have a training facility but given the current circumstances that won't be possible and would be ill advised.