I'm assuming thats the RX240 kit as you don't mention a pump or res?
all good but I'd lose the additives, plain distilled ans either a killcoil or a few drops of PT nuke will see you right, check the W/c sticky for more on dyes etc
I couldn't find the grading on it anywhere but as long as its 99.999% pure silver you'll be fine, I've heard of folks dropping a silver ring in the res so anything thats designed as a W/c coil should be of high enough purity, so I'd say yes, that will be fine
Don't grab the additive mix and dye bombs either. If you want to go for a color, either go for colored tubing or use distilled water and mayhems for dye. The mayhems already has anti microbial and anti corrosion, doesn't (from what I've read) gunk up your system, and has kickass colors to boot.
If you go with mayhems, try to get Clearflex 60 tubing, the reps at mayhems say it's worked best for them.
Also what are you cooling? Just CPU? I'm wondering because depending you may need more radiator space to dissipate your heat load