Currency bank notes' image classification

Dear ‘fast.ai’ community members,
this is practically my first shoot in applying image classification as taught by @jeremy and @rachel (Thank you to you guys). This also practically represents the very first big step for me in this amazing and full of opportunities’ world of machine learning.

For a living, I spend my days in a call center automating tasks and building SSRS reports for our customers. Tough we are not yet thinking of adopting ML in our daily operations, I aim to use what I would be learning from fast.ai and this great community, to somehow introduce these S.O.T.A techniques to better our performance metrics.

But first steps first:
As there is a bit of time, It would be much appreciable if someone could glance at this classifier and let me know of any possible way to improve on this model’s features and even on the way the code is segmented.

Thank you and long life to fast.ai.