batboy is correct that copper may be a few degrees C cooler than nickel plated copper. The plating is very thin. I believe it is mostly for appearance. However if you like the appearance, it shouldn't make a massive difference in your temperatures. According to EK, the performance is
identical. However they do not disclose any testing methodology.
Velocity is the newest block from EK. Not sure if they make as many EVOs any more.
Can't tell you much about the TT res, I use one made by Radikult and am very happy with it. You can look at his products on eBay. EK will sell you a longer tube for your resevoir,
here. XSPC also makes tube reservoirs from glass, which is kind of cool. Singularity for very high end, hand polished etc.
Fittings: It looks like you plan to use the Y valve for your drain. I personally haven't used EK fittings, but they are well regarded. I use some rotary fittings from bitspower and they are very stiff. I was extremely impressed by the quality and fit and finish of them. The rotary parts are very stiff, due to the use of multiple high quality o-rings. Yes technically each is a point of potential failure however, so it is worth considering. If you do choose to use bitspower (or other non EK) fittings, please note that some people have had compatibility issues using large bore hardline tubing with the Velocity blocks. There wasn't enough space to tighten the compression nut down on both. An extender or angled fitting solved this. I'm not certain that this isn't a problem with EK fittings as well, but the cases I saw used a different brand. Also in general with fittings, more is better. Once you get into the build, you never know where it might seem better to have a different fitting. At the end it is frustrating to have a moderate amount of expensive fittings unused, but really getting a couple more of each fitting than you expect to need will save headaches during your build. Nobody every said this hobby was inexpensive
.
Fans: I have Vardar fans (I bought them because they were the only SP fans I could find that were all white), and I love them. Not perfectly silent, but they are quite good at lower RPM. Higher RPMs they can be loud but they are moving a lot of air.
Rad: 38mm will be plenty for just about any single CPU with a 480mm rad.