Yes USB 3.0 is compatible. Data speeds of USB 2.0 are already more than enough for reliable reading and writing. You should be OK with any of the newer USB 3.0 drives.
As long as you are using analog outputs the sampling rate does not really matter. But if you plan to use the MADI card for output, it is best to have all the songs at the 48kHz for your Soundcraft console.
The good thing is that you can choose the sample rate of 48kHz in uTool for each song. uTool will export 48kHz song to the drive, without changing the source files.