The zero-separated items are standard in ID3v2.4, won’t do harm in ID3v2.3, so it’s no bad choice. As long as you save tags as ID3v2.4, you’ll be fine with this 🙂
Pictures saved within files works quite well with Firefly (iTunes as a client will show them in the “Currently playing” box in the lower left). Haven’t tried links yet – full links are probably a bad idea, relative links /may/ be better (not sure though if the standard recommends anything about the slash vs. backslash thing to make sure Windows-tagged files would still work on a Linux or MacOSX Firefly there).