Is this kit all thats needed to get a supra to 450/550whp?

Yes. That other guy must have been hiding under a Rock for the past 15 years or so. 2JZ's have been pumping out 1000+ HP at the wheels on stock internals for years now. If the Kit advertises that, check on it. Join a Supra Forum. They should be able ot tell you if the claim is legit. It's very easy to do with these motors though.

Sounds pretty complete to me. Depending on the mileage on the engine now, you may want to put new seals and gaskets in before you add that much boost, but no internal engine parts need to be changed.

you will most likely need to replace your exhaust if it is stock, a few things I would recommend getting as well so you don't blow your motor. a few gauges, you will want a wideband oxygen sensor and gauge to keep an eye on your afr's, and egt gauge and sensor. also your gonna need a boost controller. also your gonna be pushing your stock injectors pretty hard even at 445 that's over 80% duty cycle, If it was me I would get also get a fuel pump, a fuel pressure regulator and some 720cc injectors, then you won't have to worry about running lean at WOT and detonating your engine. a better form of engine management wouldn't hurt at this point either.

most every one is right but you also need to get high flow fuel rails bigger fuel pump and bigger injectors, cant boost more air without pumping more fuel.

sounds like a nice kit but i would seriously consider if your engine in stock form can handle the power upgrade. that much boost is rare on a foreign car motor as they just cant take it ( goes for some american models too) this is generally why tuner/ricer turbos are around the 8 to 12 psi range. not like 15 to 25 like youd see on a V6 or V8 (both american). you need to be looking at everything from harder head bolts to main bearings and everything inbetween as your about to put a seriously load on them with that much boost. dont forget your gonna need to retune your feul injection systems too. plus a puter upgrade to keep all the ratios like air/fuel correct through your boost ranges. a kit with this kinda power upgrade on this particular car is gonna comlicate things as compared to just putting on a turbine kit with say 100 added horsies. you may even need to add whats known as a " web girdle " which is a plate of steel made to be installed between the pan rails and oil pan. this plate stiffens the bottom end and helps keep your main caps and bottom of block from 'flexing' under heavy loads. not trying to shoot ya down here but ya just cant go adding kits like this to stock motors. theres a reason they make billet cranks, forged rods and pistons! even your rings will need to be replaced to take the higher cyclinder pressures and heat. dont forget larger valves and maybe a port job to handle the flow. bigger plenum too! good luck with project though, see ya on the street!