I store my media library on a 4TB 4x 1TB SSD RAID0 connected directly to my laptop via Thunderbolt 3 (10 Gb/s real world transfer speeds). Any changes to that drive are added to a 5TB HDD daily. I play directly from the RAID0, via iTunes on my MBP, through a pair of HomePods, when I'm at home. Lossless files are stored as ALAC. Lossy files are stored as obtained; if created locally, AAC 256.
Until now, I've been manually creating AAC versions for my iPhone SE, to avoid transcoding any of the mp3 files I still have. For sorting ease, I prepended all such album names with "AAC ". I learned from a Sound Science thread yesterday that iOS uses AAC for all system sound, so I'm not actually avoiding the transcoding I thought I was avoiding. Therefore, I'm planning to delete the AAC version of those albums, and to change my sync setting to automatically transcode higher bitrate file to AAC 256 to simplify the process. Key takeaway:
There's no benefit to paying for the extra storage required to keep higher (than AAC 256) bitrate files on my iPhone, especially considering iPhone storage is among the most expensive NAND memory sold to consumers.
I also have a Cayin N3 w/ 256GB microSD card dedicated to my live Grateful Dead library, mostly lossless. Though still a work in progress, I've spent far too many hours curating the collection to start again from scratch, so it gets an extra backup, which I store in a DAP. (It's worth noting that even though most of my Grateful Dead discs are HDCD, I only ever extract the 16-bit files before storing the physical media.)
I have a Pioneer XDP-02U inbound. It supports 2x (at least) 400 GB cards, so it should hold most/all of my music in lossless format (where available), and will serve as a backup. I'll also use it as my primary source/player at work, not because of dissatisfaction with my MBP, but because if I'm going to get tangled with the cord when I, for example, roll back from my desk, I rather it be the DAP, not the MBP, that is pulled from the desk. Since I'll be able to control the DAP from an app on my phone, providing the same convenience as wireless playback from my phone, it will probably also be my primary mobile music player. For actual wireless (BT/Airplay), my phone and my laptop will remain best options.
Except for my main library, I only keep lossless files on devices if those devices are serving secondary duty as backup storage. Except for archival purposes, there's really no benefit to having music files with bitrates exceeding 256 AAC (or 320 MP3). 256 AAC is audibly transparent to human listeners, indistinguishable from lossless during playback. Even if you have the one in a million pair of golden ears to resolve the difference, you would have to be listening so carefully and critically to not miss the artifacts (that no one else can hear anyway) that it would be exhausting and not enjoyable.
@joefig44 What is the appeal of FLAC for you? Are you using hardware that doesn't play nice with ALAC? My own experience is that ALAC is the much more convenient equivalent to FLAC on macOS/iOS. Or are you obtaining your music as FLAC, and the song files stay in that format until they get moved to one device or another?