Don't be sorry for the questions......and it's not like I've been doing watercooling all my life. Far from it....but have had at least one system under water for almost 3 years now and in several different configurations. (It's an infective hobby that conspires to empty your wallet and bank account as fast as you can fill it.)
There has been shown to be no difference between the copper topped HK 3.0 and the POM topped version. The only difference is the top.....the internals are exactly the same and both will perform identically. The difference is in the cost and weight, with the copper top version weighing a lot more. Then there is the bling aspect, and quite a few people like the copper look over the POM. Personally, I'm a bit cheap sometimes and I bought the POM version. I've got it on a Q9550 running at 3.8GHz right now @ 1.2V, and it holds idle temps right around 30C, sometimes a degree higher, sometimes a degree or two lower. My pump is a DDC2, or the MCP355, but the older version. What's out there is the newer DDC3.2, but still called the MCP355, well....as long as you're looking at the Swiftech branded version.
(I know this is confusing......Swiftech, Danger Den, and other sellers rebrand Laing pumps under their names. The two pumps rebranded are the Laing D5---Swiftech calls it the MCP655, and the Laing DDC3.1 and DDC3.2---Swiftech calls these the MCP355 10W and 18W versions respectively. Danger Den does the same thing.)
On my DDC2 pump, I'm using an XSPC top. It's a very popular top and gives a good performance boost. The best top, though, is still an XSPC top but the reservoir XSPC top for the MCP355 pump.
Here's an XSPC reservoir top for the DDC3.1/3.2 pump.
This top is probably the most used and best addition to be put on top of a DDC/MCP355 pump.....highly recommended.
As for full cover blocks for video cards, it's very variable. A lot depends upon whether your GTX 260 is a reference or non-reference design, what price range you want to stay in, etc.
Personally, I've purposely avoided video card cooling blocks since, almost without exception, what you buy for one card will not fit the new card you'll invariably buy when you upgrade, making it necessary to repurchase a new video card cooler and then have to sell the old one.
And reselling a video card top tends to make you eat a lot of your investment.....as in you lose at least 1/3 of what you paid, maybe up to half. I did it once, then resisted the temptation when I upgraded video cards....twice in 6 months. Just couldn't stomach spending $100+ over and over for new full cover blocks when I upgrade video cards at least every year....sometimes more often.
At the same time, I've upgraded cpus, too, and my cpu block just transferred from old to new cpu. MY HK will even move to a Socket 1366 when I move to that.....HK has a mount kit to change the mounts to fit the new socket. So, my investment in my cpu block will be long lasting. GPU full cover blocks, on the other hand, rarely are long lasting.
Anyway, given that diatribe, HK gpu blocks are the hot item. EK blocks are quite popular, too, as are Koolance. My suggestion is to read, especially on XS's forums, see what's working for most people with your particular card, then make your decision.
Tubing......the brand most tend to recommend these days is Primochill Primoflex Pro LRT. Clouds the least in use, good flexibility, has anti-microbe properties.
This the exact tubing I'm currently using....good bend radius, love the stuff.
An HK 3.0 cpu block with an XSPC RX radiator, an MCP355 18W pump with the XSPC reservoir top is an excellent setup and will easily stand adding a video card block to the loop. But be aware, gpu's run hot and adding the gpu to the loop will raise your idle temps of your cpu a tad. If you are planning to add a video card to the loop, I'd really suggest looking at the RX480 radiator instead of the RX360......you'll have extra cooling capacity you will be definitely need and use when you add the gpu to the loop.
But, please, inquire with others about this. Aigo is the expert around here.....I'm just a hobbyist.