It would follow the fundamental’s of a Orchestra
Starting class = Instrumentalist
Tier 1 = instrumentalist, Woodwinds, Strings
Tier 2 = instrumentalist, Woodwinds, Strings, Percussions, Brass
Tier 3 = Woodwinds, Strings, Percussions, Brass, Conductor, Singer
Tier 4 = Percussions, Brass, Conductor, Singer (another two related music class)
Tier 5 = Conductor, Singer, Tuner (another Three related music class)
This is all I have so far 
maybe others might be able to add more but as you can see the idea of each class is based around the instrument they play and branch out from there what’s everyone else’s thought’s on this
Also to add there special crafting class will make musical instrument’s and improve them because it is the tools they use that can enhance them I guess you could call this class a tuner.
The skills I have in mind are just off the top of my head so please try to understand haha.
Instrumentalist ability’s would be the attack ability’s of all the classis.
C1) Soundwave targeting ability each level increases the AOE range starting from the target at lv 1 to 15 cells around at lv 15 but deals more damage closer to the target area
C1) Shock wave blast of sound outwards in a cone form you pushing targets away dealing small damage each lv on the ability increasing the push back.
C1) Tone death detaunts the enemy skill level increases the chance to work.
C1) Luring sound makes enemy’s slowly walk towards you skill level increases the chance to work.
C2) Catchy tune makes enemy vulnerable to physical attacks from behind.
C2) Mesmerising tune makes enemy vulnerable to magical attacks from behind.
C3) Choir doing damage based on how many party members next to you
C3) Cheering has a chance to remove one debuff from all party members
Now the next part is going to be odd with the Woodwinds and strings class so bare with me they will be buffing a aspect but debuffing the other basically increase one but take the other one away.
C1)
Woodwinds core stat buff ability increases 2 CON but reduces 1 SPR each level.
Strings core stat buff ability 2 SPR but reduces 1 CON each level.
C1)
Woodwinds Regen ability has a regen to HP but slows the SP regen each level.
Strings Regen ability has a regen to SP but slows the HP regen each level.
C1)
Woodwinds Elemental resistance ability to Lighting 5% but reduces resistance to Earth 2.5% each level.
Strings Elemental Resistance ability to Earth 5% but reduces resistance to Lighting by 2.5% each level.
C1)
Woodwinds Buff to casting speed is speed up at the cost of ability’s costing more.
Strings Buff to lowering the cost but slowing down the ability cast time.
The reason for the debuff is because when two instruments are played together the song change’s completely you loose half the buff but you also loose the debuff unfortunately I have yet to come up with the rest of the ability’s but this is to give you somewhat the idea I had for the class that they can be a double edge sword on there own but a boon if working together.