I used to be involved in fairly high end car audio. My last project involved 3 amplifiers, 2 sets of front components, rear speakers (for fill only) and dual 12" subs.
One thing I will tell you is when you start getting in to GOOD speakers, like front components, 2 way or 3 way in the $600.00 range (and up) they have very different sound characteristics and it may be difficult, but the best way is to listen to them if possible.
Focal is my preferred brand. Some folks find them a little bright, but at this price range they usually come with an adjustable crossover.
You will probably have to change the deck as well. In general, the factory stereo is weak and will not drive higher end speakers very well. Just throwing new speakers in the car will not work out well for you.
When choosing an amplifier, look at the number and size of the fuses. if a 1000 watt amp has one 20 amp fuse, it is not 1000 watts. It should have 3 or 4 30 amp fuses.
Make sure you take the car to a GOOD shop. I can only imagine all the electronics connected to a 2013 BMW.
I;m sure someone will mention this, but this forum is not really what you are looking for. There are MANY large car audio forums and you will have much better luck on them.
Best of luck with your project.