Is it a bad/good idea to take calc BC this early?

To preface: I did Calculus AB in 10th and BC in 11th. My school policy is that students take AB then BC, and the teacher for BC assumes you already know all the AB concepts when you come to BC. You should ask around students who took BC or the teachers and make sure your school's BC teacher(s) knows that the students are taking the class with little/no prior calculus experience.

Another thing to consider is the predicted course load you will have if you take both BC and Statistics the same year. Is the teacher someone who gives a lot of homework, do they prepare you for the AP exam, are they someone who is understanding about late work etc. are questions you should probably ask to students who took the class.

Also, if you don't plan on doing a math heavy major in college, and are doing this for your interest, then consider the fact that getting a 5 on the AP exam in 11th grade would be better than getting a lower score in 10th. If you are confident in your math abilities and love doing it, then go for it! If math is something you don't particularly enjoy, then it might be better to wait a year.

It is indeed always worth it to take as many math classes as you can. The earlier you take calc, the better. However, if you aren't 100% confident in your math skills then it is a good idea to relax a bit before taking Calc BC, as it is the hardest and most detailed math you can take in an average high school.