If you have a Raystorm, you can look at the XSPC website and if nothing there, go to a review such as one at Martin's Liquid Lab where he takes it apart.
I think you can probably get by with flushing and looking through the ports if it is new. After using it for a year, you may need to clean out plasticizer. You will need the proper tools and will need to know whether you are voiding warranty so you can weigh the pros and cons. Other than that, I find it helpful to have a spare O-ring in case one tears. And I like a tiny tube of O-ring silicon sealant like is used for the backpacking pumps (so can probably get it at hardware or sporting goods store). Vaseline is discouraged on rubber but a tiny amount of sealant can make the O-ring a bit sticky to hold it in place.
Anything can leak during re-assembly when you don't put it together the way it came apart or when the O-ring tears (happened to me putting on a new top on my Apogee XT v2). But you can test it using the flushing method (pond pumps).
I do not use Pre-mix but some do. I use silver + distilled. I think your kit is all copper and I don't think XSPC voids warranty for not using their coolant like EK and Koolance do but you might check. Maintaining warranty or using it in a mixed metals environment would be the only reason to use proprietary coolant as far as I can see. You may be able to send the coolant back if you go with distilled and silver. I don't encourage dyes but if you want it, then check out the Mayhems club in the forum for good information. Good luck.