Keep in mind that the actor cast as Maglor will need to be a talented singer. Preferably someone with a very strong voice.
He is often characterized as the 'kinder, gentler' son of Fëanor, and it is true that he has some redeeming qualities. But keep in mind that he takes part in multiple battles and kinslayings, so he's definitely a strong fighter as well.
Here's some artwork by Jenny Dolfen for inspiration
Maglor as the talented but tormented musician:
"The Harp No Longer Sings"
And here we have Maglor as a reluctant leader, thrust into the responsibilities of leading the Fëanorean camp after the death of his father and the capture of Maedhros.
"Sealing Maedhros' Fate"
"Brothers"
And the *main* reason he's often considered the best of his brothers - he decided to foster Elrond and Elros rather than, say, murder them.
"As Little Might Be Thought"
Jenny Dolfen's page can be found here:
https://goldseven.wordpress.com/galleries/tolkien/
And of course I can't help but also include the artwork of Catherine Karina Chmiel (Kasiopeia):
Maglor and Maedhros:
Watching Maedhros relearn how to use a sword with his left hand:
"And Maglor Took Pity Upon Them"
"Captive" (Maedhros is the foreground figure; Maglor is in the background)