It wasn't as complicated as you might think, but very time intensive.

Suit:

• Red jumpsuit, covered with red latex body paint to get that rubbery texture/look. I also took off the pockets to get a uniform appearance. Worth noting that you'll want to get some of the top coat gloss body paint stuff, too. I didn't put any on, and that suit stuck to itself like a motherfucker.
• Suspenders were basic, black work suspenders from Home Depot.
• Nylon belt and ammo pouch came from a local gun store.
• Bandolier was from an old, nylon tie down, spraypainted black.
• Boots were basic PVC work boots from Home Depot.
• I used a piece of MDF spraypainted black to bolt the tank to, in the back, then superglued it to the suspenders.
• Made a cowl of sorts out of black spandex to cover the area between my shoulders and the gas mask.
• Gas mask is a Cold War era Soviet mask. Black ones are harder to find, and I had to take a hacksaw to the 'snout', then covered it with a piece of plastic I carved with a dremel. The side filter is an empty can of ham, painted black and gray. The nub on the other side is a regular nut, then a rounded tip nut, glued to each other, painted, and glued to the mask. Also bought some 25% window tint, then cut it to fit the lenses.
• Incendiary grenades are PVC pipe, cut to length. Put flat plastic PVC caps on either end, and then a square 'nut' threaded cap on one end. Cut and bent some aluminum for the spoons. Glued the spoons to the 'nut', then the grenades to the bandolier.
• Gloves were black heavy duty PVC work gloves, with the finger tips cut off. Then I put regular yellow household work gloves inside, and glued them in place. I originally wanted some 'real' firefighter gloves, but they're rather expensive.

Tank:

• Air tank was just 6 inch PVC, cut to length, then capped at either end, glued and painted.
• Pressure gauge is a cheap tire pressure gauge from the auto parts store, glued to the top of the PVC cap.
• The tank was bolted to the MDF, but I glued the remainder of the nylon tie down I used in the bandolier to look like straps.
• Side bottle is an aluminum water bottle, bolted to the main tank with toggle bolts.
• Valve on the tip was a plastic hose valve, cut to fit, then painted and glued in place.

Flamethrower:

• Flamethrower tank is a Winchester propane tank, about the smallest you can find that still maintains the distinct shape of larger tanks. Still weighs almost 12 pounds empty, so the flamethrower is NOT lightweight.
• Gas pump was a refurbished model with red grips, bought off Amazon.
• PVC pipe used for the two main pipes on the body of the flamethrower, same diameter as the grenades.
• Stereo wire painted red and yellow, taped to the underside of the gas pump with black electrical tape, then glued into one of the pipes.
• Pilot light assembly was copper tubing, set inside the length of one of the main body pipes, then glued in place, bent and spraypainted black.
• Pilot light itself was the tip of the gas pump nozzle, cut off, then glued in place with a piece of light blue paper crumpled and rolled up to look like the flame.
• Muzzle shroud and airblast shroud were 32oz restaurant style plastic cups, carved with a Dremel, then spraypainted black.
• Hose clamps used to hold the whole thing together, also spraypainted black. Liberal amounts of superglue and epoxy were also used for structural stability.
• Bent the PVC pipe just before the muzzle shroud by heating it with a blowtorch. It leaves a sort of kink in the plastic where you bend it, but was the best I could do.
• Hose to the gas pump was a replacement propane grill hose, cut to length, and then glued to a threaded nut on the far end, which in turn screwed into the gas pump handle.

I think that pretty much covers all the parts. In total, I probably spent ~$500 on materials, so this was one of the more expensive costumes I've ever made. Also, I live in Texas, and this thing is a damned sauna to wear around, so be careful if you make one and wear it around. Drink LOTS of water, etc.

EDIT: Formatting, forgotten bits added.