There is no limit to how much data you can connect to your account but we recommend having at least 1000 rows and 5 columns in case your use case is AutoML. For Time Series, having enough data points such that after aggregation (hour/day/week/month/quarter) the number of rows is not below 12.
In general, connect all the data that you have since machine learning is all about learning patterns from the data, so if you keep data away then your model will not be exposed to all the possible patterns in your data. This will in turn affect the performance of your model when used on real life data for making predictions
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