The Turbosmart 800 is a very small reg, 800hp at the engine is pretty close to your 500wkw mark. I would usually recommend the 1200 at that power, the added an fitting upgrade is worth the extra $40 dollars over the 1/8bspt imo.
Surprisingly the stock fuel lines should be just large enough for 450-500kw, but the 044 won't make it there. I would be picking up a Walbro 460L and dropping the pressure a little if your injectors are large enough, you might get close.
Most installations I block the mid rail return, one feed line is more than enough. I assume you have a Freddy plenum?