(1) Yes, there are separate settings in the Function menu that let you adjust (a) the overall volume of the style being used, (b) the overall volume of the MIDI song file being played, (c) the overall volume of the groove pattern being used, (d) the overall volume of any audio coming in through the AUX IN connection, (e) the overall volume of any audio coming in through the two USB ports, and (f) the individual volumes of the Main Voice, Dual Voice, and Split Voice. Note that you cannot adjust the individual channels of a style, song, pattern, or incoming audio signal, only their overall volumes. Once you've got the balance the way you want between the volume of the keyboard's voices and the volume of everything else, you can use the MASTER VOLUME knob to adjust the total volume.
(2) No, the PSR-E463 does not have the ability to play "audio styles" similar to some Yamaha models. You can play along to a pre-recorded audio accompaniment if you want, but the keyboard doesn't have the ability to let you control the audio playback the way you can control a style, switching between different keys and chord types, or alternating between different loops and fill-ins and variations.