So, I didn't see the melodious deck. I will admit, I have played the deck extensively in MR3. That being said, here's my feedback on it.
You keep having a tendency in putting your play starters at less than 3. This is something you should stop doing. Always put your play starters at 3.
1st Movement Solo needs to be at 3. Same with Ostinato. Ostinato let's you go into Schuberta the Melodious Maestra by sending Aria the Melodious Diva and Elegy the Melodious Diva to the GY which at the end of your turn, let's you create an "unbreakable" lock.
Celestial Transformation can help create your lock as well if one of your monsters are in the hand. It WILL attempt to destroy the monster at every end phase which Elegy can prevent. This card can also let you play Kristya which can prevent your opponent from Special Summoning as a 1 turn Vanity's Emptiness.
Photon Lead is the same thing as above, but doesn't halve the monster's atk or attempt to destroy. It's also strictly Level 4 LIGHT monsters.
Valhalla this card can let you play your fairies from hand if you have no monsters you control. This can let you cheat out Mozarta which can let you bring out another card. You will have to choose between this, 1st Movement, and Ostinato and pick the best option depending on the situation if you have all 3.
Now let's talk about the extenders. Run your extenders at 3. Again you for some reason choose not to. Canon the Melodious Diva, Sonata the Melodious Diva these can let you go into your Link 2 with EASE, the greatest of EASE.
Now as for a problem with some of the card choices. Crystal Rose, it's not a good card. You cannot convince me it is for Melodious. Mozarta is fine to run as a 1-2 of. Any more than that and you risk opening doubles more often of it. Which is bad for consistency. Solo the Melodious Songstress is also really bad as it requires your opponent to have a monster and you don't, which also conflicts with 1st Movement, Ostinato, and Valhalla.
Soprano is a 1 of if that, only because you only gain its effect on Special Summon, but being able to bring it out from their Link isn't too bad, which can let you fusion outside of Ostinato or Poly. It's not a card you want to open multiples of.
Opera, like why? You can make an "unbreakable" board without it. It does nothing for the deck.
Score is a hand trap, and it isn't even a hard once per turn, you can run this at 3 while also running Honest.
Tamtam, I see what you're doing by searching Poly with it, you have the right idea of running it at 1 just like Soprano should be run.
Serenade, is cute and all but only getting the extra normal summon after she was special summoned is really bad. I wouldn't run her.
Shopina doesn't do anything and locks you into light monster's effects which is really bad since you can run some hand traps like Ghost Belle (which can stop stuff like D.D. Crow and Called By or even stop Gamma).
I already spoke on Dimensional Prison, it's too slow. Stop running it. Also Melodious Illusion is really bad Your unbreakable board won't need that kind of protection.