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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
For database, when you feel ready to, give a shot to MongoDB, you can use it with Node.js (Mongoose) and your languages C# (Nuget) and Python (PyMongo) too.
I'm pretty sure JavaScript won't be a problem for you, I'd like to suggest you to have a look on Node.js as it's pretty complete and use JS for backend and will be a great asset to have.
NOTE:
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Hence, a higher number means a more popular project.