Is this frowned upon?

It depends. If you're doing it just for yourself bc it's fun that's awesome, but if you're doing it at like a con just because you want people to see your original designs and think you're a special snowflake then you're going to come across as self-entitled and snobby. It's not really frowned upon, it's just that most people at a con won't get it or understand your cosplay, and most people KNOW that you know they won't get it and that you want people to ask about your character just so you have a chance to talk about how special you are and how you designed it all by yourself. Plus Neko is already pretty popular so I could see why she'd dress up as her, Rin/Len's voicer does the same.

Wait, what color is Irene's hair? I found a wig meant for Miku (with her hair down, not in twin tails) that might be that long.
I can try to find it again and link you to it, but I'm not sure if their hair is the same shade

Ara, that'd be lovely! You can sorta see her hair in my avatar :3


Hihihiiii it's gonna be hard, but... I hope to do this someday :3 You're gonna have to help me with the details! >w<

Here's one
Here's another
And here's the last

They probably aren't all the right length or color, but that's all I could find DX
Must be that wig I was looking at was sold out :<
I don't know if the US Amazon site ships internationally, either... But the sellers probably have their own websites

This one looks the like Irene's hair :3 :3 :3 :3 And actually I also want to cosplay as other people UTAU too *_*

Dude hecks yeah!!