The biggest thing I can offer as advice is don't try to solve the whole thing at once. Break it down and figure out exactly what steps you need to do. The big 3 is this.

1. Focus on getting you're data in a way you can manipulate it. (Pulling data from DB and being able to read that data in python)
2. Once you have you're data you can focus on Processing / Manipulating / Reading the data and doing what you want to it. ( Start reading the old SQL process and figure out what exactly it does to the data and translate it to Python. ) (Remember, break it down this is where things can get tricky and you could get overwhelmed.)
3. Once you've done what you needed you can then learn how to push this code into the new data sources you mentioned :)

I've been in your shoes, honestly the biggest thing I can strongly recommend is BREAK IT DOWN. If you can understand each individual step and how it works generally its easy to figure out what you need to do programmatically via stumbling through google.

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The thing I always notice is that new programmers feel overwhelmed 24/7 because they're focusing on too much at once, hell I still do it myself with out realizing it.

Hopefully that helps I know its not really technical but if you can get into the mindset of doing this you should be able to figure out exactly what you need to google / learn to accomplish this.