I don't know of any "Nasties" an SS coil could give off, certainly not at vaping temperatures, discolouration of the wire isn't a significant issue - or even really an issue at all - I'd be more worried about running at high wattages - vaping very hot builds does increase the risk of inhaling thermal decomposition byproducts like formaldehyde from your juice, but even then that only reallly becomes an issue if your straying into the territory where you start to get dry hits.
That's fairly hefty wire you've used there - for reliable TC you need to get your builds higher in resistance perhaps a thinner guage wire would help. Also you'll find Smok mods are pretty poor at TC as is the Fuchai. I'd also advise against using a sleeper build - with that velocity style deck it simply isn't required, just build two normal coils and install them...
