I did last year basically the same thing you did now.
I ripped the entire interior out, top to bottom, and installed KilMat on everything.
Built my own sub box, whole new system, separate amp, the works.
The point is, I did go to the trouble to make the environment worthy of the new experience.
So, my entire musical inventory for the car is now on Flac, on 3-4 32G flashdrives now.
I have a converter program that will do mp3's and other lossy and lossless formats as well as Flac.
So when converting to a particular format, its just what box do I tick, they're all there for the choosing.
But Flac is totally working for me, I have no complaints and everything is good.
Would I notice the difference between Flac and mp3's?
I don't know, maybe not, I've subjected my ears to some pretty substantial musical abuse for +/- 40 years, so who knows.
But it's just as easy for me to convert to Flac as it is to convert to mp3, and flac is lossless, so I chose Flac.
Its literally, do I tick the Flac box, or do I tick the mp3 box, its that simple and easy.
I actually doubled my musical catalogs on both Flac and mp3 on my home drive storage, so I have everything on both formats.
I mean, its just so simple and easy, why not?
But I never use the mp3's for whatever reason.
Not as much space per flashdrive, but that's just such small potatoes, it just doesn't matter to me.
So I have to carry an additional flashdrive to make up the difference...big deal, so I go lossless.
To modify or make a new flashdrive of music takes not even 5 minutes now.
It's all folder-based, exactly like opening a new folder in Windows, no different.