I've converted many systems in my life and I have always found it best to use the old system as a guide and not try to use anything from the old system at all. Know what it is that you are trying to do, understand what the inputs and outputs are, and write new code. The old system would therefore be a guide as to what these inputs and outputs are, in other words, it defines your use cases.
With that said you haven't mentioned what DB your old .NET system is using. The only DB I ever use anymore with Django is PostgreSQL, it is also supported better than any other DB.
I do consult work specifically for these types of cases.
~Carl
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Carl J. Nobile (Software Engineer)
carl....@gmail.com-------------------------------------------------------------------------------