When playing the accordion we have to understand that the key is to balance the tone of the treble and bass. Generally you need to find a bass sound that compliments the treble. The bass should not be overpowering or weak, nor too high or low pitched. Unlike on the piano, we accordionists do not have the same independence of volume control of bass and treble, due to the bellows supplying a single reservoir of air to both the treble and bass reeds. Therefore, you can fine tune the balance using the bass switches. Usually the treble keyboard, which in Scottish music will be your melody side, should be slightly more dominant, but with the bass coming through clearly, with a little bite - but not too aggressively. The bass is your rhythm section for keeping the tempo steady. So your melody will need to be in synchronisation with the bass. Lead with the bass.
In Scottish traditional (dance) music, usually the musette (+8', 8', -8') will be the treble voice on marches, jigs, reels, strathspeys etc. On waltzes the cassotto clarinet voice is nice at times. When using musette voice the master bass switch or some of the slightly lighter bass voicings should work fine (but not too weak or high).
But really you need to hear what the accordion sounds like, and how it suits your tunes. I don't know if you are an accordionist or not, but if you are going straight from piano to piano accordion - they are quite different, and there are subtleties to phrasing, articulation and getting a lift in the music. A purpose built musette accordion will have a selection of bass switches that you can use to compliment the various treble voices. But you must understand this is not a free bass accordion (with classic/double octave tuning) or a piano - so it will not really have the same homogeneity of tone from treble to bass like on a piano. The bass tone is quite different to the treble on a musette accordion (on most switches) because of the detuned nature of the +/- treble voices (you would not want a detuned musette sound on the bass). All will become clear when you receive the instrument...