There's a few examples on tying a turban in this video. The 3rd one is close to what you want.
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For the robe, there are a few options. Hindu clothing is usually very cheap and made from cotton or linen. If you get the plainest ones, they usually look exotic without having a definitive ethnic feel.
You can go for a Sherwani
Or a Kurta
You could also go straight for the source and go Bedouin. Most places that sell bellydancing attire sell men's clothes, just ask for a Galabeya
I've seen them long (ankle lenght) and short (mid thigh), long and short sleeves.
Since you are going for the non-ethnic, fantasy type, you can combine pieces of basically anything you want, as long as they look the part, including Mongolian clothes.
Pattern here:
Mongolian coat
"Never violate a woman, nor harm a child. Do not lie, cheat or steal.
These things are for lesser men.
Protect the weak against the evil strong.
And never allow thoughts of gain to lead you into the pursuit of evil."
-The Iron Code of Druss.