Can I point out some very real flaws with actually making a working flamethrower unit for a gauntlet.
1) Even if your armour is made from metal, your flightsuit is going to be cotton. Add to that leather belts, cotton half cape, boots, vest, mowhair rope belt etc etc - ALL flammable. I have seen the footage of a few people using real flameunits on their suits and in my opinion they have been very very lucky not to set themselves alight. If your armour is plastic then you'll simply melt it on you making the whole situation even worse.
2) With a Mandalorian helmet on your field of vision is cut down considerably. Not as much as with a Stormtrooper, Clone or Vader but still enough for you to have to spend some considerable time getting used to (even after 2 years of trooping on a very regular basis I still occasionally walk into small kids that appear below my field of view). This means the potential is there to miss what you are aiming at with the flame unit.
3) Any and every police force in the world would consider it a dangerous concealed weapon (one with the potential to blow up on the user) and would arrest you on sight.
4) It's bloody stupid!
My advice - Make a great Boba, Jango or Mando costume, have fun doing so but don't make a working flamethrower.
A surprisingly short forum on the Boba Fett Flamethrower...
More importantly, I want to set the record straight. No offense, but the above advice is from someone who obviously has no real experience with fire and flame making. I've built a few full-sized flamthrowers that can shoot about 7-8 meter flames of alcohol or gasoline. I use gasoline responsibly to light fires. I simply understand the items I work with and how flammable things really are. I got the plans from the guy on eBay (haven't had a chance to build it yet, but will as soon as I get back from Iraq). His design is a bit difficult to understand, but I'm sure once I get the materials in front of me I will have no trouble.
I will agree that cotton is flammable, so you would be better off keeping anything from the elbow down made of something less flammable or possibly giving it a coat of fire retardant spray (should be easy to find during the holiday season). Leather is no problem, you might catch it on fire, but it won't hurt you or burn through a work-leather glove. Plastic is going to depend on the thickness. It may catch, but again won't melt unless you don't put out the burning fuel on it. Metal is obviously good to go as well. I'm sorry I'm not more knowledgeable on the costume, I just found this forum through google as I'm a pyro, and wanted to spread my knowledge. The thing to remember is it is the fuel that is burning so unless the item is really thin, all that happens is the fuel burns on the surface of the item (cotton will catch, leather will not). Be aware of any paints used as those might catch on fire.
The helmet thing... probably a good idea to take the helmet off when lighting up.
Police... if you are using this thing in public, yeah you're stupid and probably will get arrested. If you are using this at a private residence then the police shouldn't be bothering you. If it's really a concern then talk to your neighbors before hand and explain to them what you are doing so they won't be alarmed if they see you shooting fireballs in your backyard. The laws in the US vary by state (I know for a fact that Texas has a law against a flame propelling device), but there is a difference between a novelty item and a weapon. A novelty is something that doesn't leave your property, where as a weapon is something brought into public (yes, loose definitions, but that's how people get away with "collector's items" such as butterfly knives) It is presumptuous to assume that "any police force in the world would arrest you on sight" for this. We don't all live in the UK.
Bloody stupid? Certainly not. People are stupid, not objects. Even a toaster in the hands of a stupid person becomes dangerous.
Please don't make such claims if you have no experience in such matters. Feel free to ask me questions!