I’d say since you’re a beginner, it’s much better to try to implement your regression functions and any necessary helper functions (train/test split etc…) yourself in the beginning. Learn the necessary linear algebra and quadratic programming and try to implement linear regression, logistic regression and SVMs using only numpy and cvxpy.

Once you get the hang of it, you can jump straight into sklearn and be confident that you understand sort of what those “blackboxes” really do and that will also help you with troubleshooting.