Make sure you do research on the available safety features and decide what you want, but never use them as a crutch. Your brain and your trigger finger are the final defense against a negligent discharge. Also keep in mind that manipulating features such as a thumb safety will need to be incorporated in your training regimen. Personally I strongly advise against a magazine safety, and I don't like thumb safeties either.

As far as drop safety, i.e. gun going off if the gun is dropped or hit with a large force, all modern firearms including the M&P are extremely safe in this regard.

I think you are picking a good caliber, 9mm, and it's very good that you are getting training. Good luck with your purchase and enjoy your new gun.