I'm far from being a god, but thanks.
It's strange that some games don't show the size at all.
The bug I had was reporting a very big size. and now you report a "no size" at all. 3.0 is weird
If you test the r1207mod01 which I linked, tell me if it fix the problem.
I don't recommend choosing WBFS format if you don't have it yet.
But if you have the WBFS, it's up to you to decide based on the fact that WBFS can corrupt the games easily (sometime installing a new game overwrite parts of another games, rendering it useless).
by looking at the table of used block, multiple games share the same "block of data", but the manager don't know which game is that data, you would have to test each of your games to test if they are full or missing files.
Advantage of WBFS is that some problematic games with FAT32 are working fine on WBFS (usually dual layered games which freeze). But NTFS is also a good solution for that problem.
FAT32 is better because you can use that partition easily on your computer for everything else, for Homebrew, Emulated Wii NAND and GameCube backup.
If you don't NEED the wbfs format for a specific reason (testing purpose, etc.), then converting is probably a good idea.