Can I install directly BIAB, realtracks, realdrumns.... on external USB disk? Or is better install BIAB on main C disk and data, songs, realtraks..on external disk?

You can install the program anywhere, and you can install the RealTracks anywhere they will fit, and you can install the RealDrums anywhere they will fit.

The program will run fastest if you install it on a local (internal) SSD or hard drive. I have all my main program, songs and styles on the internal drive, along with every folder except RealTracks and RealDrums. Those are on another drive. You just go into Preferences, RealTracks and say where they are. Same for RealDrums.