So long as the DAP supports the MicroSD XC standard, it can support some extremely large sizes. Of course, the largest available that I can recall is 200GB. On my Questyle QP1R, I run two Sandisk Ultra 200GB MicroSD cards in both my slots so the L5 Pro will be able to read the size of the SD card. As for file sizes, FLAC compression is pretty good with no perceivable problems. Most modern processors should be able to handle even high FLAC compression.
If you really want to carry everything, getting a small dry case for your microSD cards. I keep one in my EDC backpack for school and travel. There's several options available, like Pelican's SD card dry case.