Speaker & Amp Upgrades?

Currently have my e39 stripped to the bones, want to upgrade the audio and Bavsound sounds like the easiest option, but is it the best?

Electronics and specifically audio electronics is new to me.

The car currently is the bare basic audio set up (no door speakers in the rear at all, not even any wiring)

I would love to have decent audio but I'm unsure if it's worth the hassle of rewiring the whole car and then trying to figure out what amp I need and what works with my head unit 🤯

Do I bite the bullet and settle for Bav? Or do I go a little further at this point and put in a little effort to upgrade when I'm this far. Where do I even start?

Thanks in advance 🙌🏻