Hello there Traveler I'm here to help!
1. Looking for the right type of fabric for a costume like this is always tricky and though i've never gotten to make a costume all on my own my grandmother was a seamstress so i've been sewing my entire life. Anywho for Maya's costume if you don't want it to be shiny i'd go with a yellow cotton and she also has grey strips in her uniform too.
2. To make it look more professional i'd use an actual sewing machine and take your time. If you intend on making more than just this costume and don't have one it's a VERY good investment.
3. Go to a professional for your hair and take a good picture of Maya, front and back headshot, for something like this you want it done right and you want it to look good because not only does she have two toned hair but you're going to be stuck with this cut for a while.
4. In the pictures her shoes look more like tennis shoes but I don't think using combat boots is a bad idea at all. You can take the left over strips from the cat suit and yellow fabric to make a boot cover the concept is fairly simple and you only have to really worry about what peeps out from under her pants and the base of the shoe.
5. Finally, the weapon. Nerf guns are perfect for this kind of thing because even from a distance you can tell the thing is fake plus, when you find the right kind, they're easy to paint.
I hope at least a little bit of this helps, if you need anything else feel free to message me, ok?