Have a 2014 435i with HK / arm rest USB and it recognises a 1TB Samsung 850 EVO SSD formatted exfat. FLAC, and yes some mp3, and does work but..... First time hookup there was a very long scan to get all file data (4 minutes or so). Rescanning is only bout 20 seconds or so. All files good, genre, etc. When i restart car after long parking it seems to restart at diff song yet in same chosen genre (as i use genre on shuffle to enjoy music most of the time). So 1TB works, yet not perfectly. As for song qty, many, many thousands.
File system is band name folder, then album folder. Additional top folder for such things as Various Artists, or grouping Soundtrack, etc.
BTW 128GB SanDisk worked file.
PS: Enclosure said to be a known good for BMW is
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1