/cgl/ - Cosplay & EGL

Okay, so... Ah, here's the thing.
I want a little bit of help with something. This is months and months away, maybe even a year away if I can't afford it soon, but I wanted to put together something for Halloween.
It's going to sound cliche, but I want to be a creepy doll. And I was going to sort of go all-out (not like, super expensive, but expensive enough to look good.) So, I'm going to try to go for a gothic lolita coord with a monster/gore-doll twist.
The help that I need is going to be in the picture related:
>Have skirt, know it looks good on me, but need a petticoat (in purple).
>Going to go with deep purple and black as the color scheme.
>Have shoes picked out but not bought, yet.
>The shirt is what worries me.
I'm buying the shirt from Amazon. I want the shirt in picture related. Like I said, I'm not going all out, because it's for a costume, not fashion. However, I HATE the cuffs for the sleeves. Does anyone know how to cut the cuffs off to make them shorter? I want to make a new button-up cuff at about a 3/4 sleeve length. I would be adding an elastic band under the fabric so it can stretch, and over it I would like to add a deep purple ribbon with higher quality black lace attached at the end. I'll have to draw a pic for what I mean at some point.

I'm not the best at sewing; I can hem, I can fix holes, and I can hand-sew in fairly straight stitches. I do own a sewing machine, but I haven't used one in a long time. How hard will this be to fix if I follow tutorials for hemmed and cuffed sleeves?

Also... The shirt is sold by M4U, and I'm worried it is Milanoo hiding itself under another name. Then again... This is for a costume, so that's not the biggest worry if I can make it look acceptable in the sleeve department.
Should I just go to a professional seamstress?