1) I use manufacturer websites such as
http://www.dangerden.com,
http://www.swiftnets.com/, and
http://www.cooltechnica.com/. Then, I use local stores like
http://www.enuinc.com and
http://www.iguanamicro.com for misc cooling parts.
2) I don't use biocide by itself. I just use a high percentage of antifreeze. It works well to reduce biological growth and galvanic corrosion. I use 1/3 antifreeze because I'm willing to trade off performance for maintenance. I didn't change my coolant for 4 years and the parts were still squeaky clean.
3) Coolants... see #2.
4) I use 1/2" tubing just because I have it and it seems to work well. I'd probably switch to 3/8" tubing now if I didn't have a boatload of 1/2" tubing, fittings and parts already. With the newer pump Laing DDC, it has enough pressure to deal well with 3/8" tubing.
5) Pumps. I wouldn't buy anything but the Laing DDC. Swiftech uses another part number for it: MPC 350/355. It is fairly quiet, high pressure, and (most important!) reliable.
6) Radiators. I wouldn't buy anything but the PA160, at this point. It happens to work well and if paired with a single Late-Loon 120mm fan, it is quiet. You can get great performance with that pairing.
7) .... you can't count? lol
8) Cooling block. The blocks from the major manufacturers are all GoodEnough(tm) at this point. Cooltechnica, Dangerden and Swiftech all make good blocks. I don't trust anyone else though. Lapping is a touchy subject. Just remember that flat is what you want. Shiny is meaningless. A bowling ball is shiny. The above manufacturers have well done bases. A flat but non-shiny base may actually be better, as you get micro-pits for the conductive particles in the thermal paste to settle into (but don't quote me on that). Just remember: flat is king. Swiftech, Dangerden and Cooltechnica all make excellent blocks. The kind of paste you get is mostly irrelevant unless you are quibbling over 0.1C variations. I've seen a review that used TOOTHPASTE and it worked ok (it wouldn't in the long-run as the water evaporated, so this is why you use real thermal paste).