My opinion FWIW,
I would recommend looking at the swiftech MCP-600 pump instead of the ehiem. It is compact, powered by the computer PSU, and only uses 9 watts of power. It also has a pressure head of about 10 feet! That is more than any of the other aquarium pumps being discussed except the Danner Mag3 which hasn't been mentioned, yet. Pressure head is the key rating for a computer waterpump, gallons-per-hour doesn't mean much.
The whitewater cpu block is good (and you don't have to be an overclocker to benefit from it). The swiftech MCW-5000 or -5002 or the new MCW-6000 are also good. If you want to cool the northbridge, get the lowest flow restriction block which the swiftech MCW-20 (they make good stuff) . For the GPU, the swiftech MCW-50 is a good choice as is the Maze4 gpu block.
For tubing, 3/8ID 1/2OD is much easier to install and will quick-connect to most swiftech blocks. www.swiftnets.com
if you haven't been to the swiftech website. If you could keep everything internal to the case, I'd say try 3/8ID. If you have to go external, then I'd use 1/2ID tubing for lower flow resistance. External cooling boxes use much more tubing than internal and tubing flow resistance becomes a bigger factor.
Radiators......what else can be said except use a heatercore because it's cheaper and almost the perfect design for watercooling PCs. Also, use the biggest rad you can fit. More radiator size is an easy way to improve the system cooling without much expense. Some people use 2 rads. Maybe you could fit 2 smaller ones in the case, BUT make sure they can each handle a 120mm fan. Use a good fan shroud for each rad, they really help focus airflow throught the rad. The little 80mm rads won't come close to handling the heat load you'll have; 4 or 5 of them might be enough
The 80mm rads main advantage is they are small, cute, and much easier to fit into a case without mods or hard work.
As far as running nearly fanless in the case, that is a big job to do right. You'll have to cool the mosfets, southbridge, northbridge, cpu, gpu, psu, hard drive(s), and anything else that gets even warm with normal case airflow. That is a very custom water system and IMHO you aren't ready for that yet. It can be done but is alot of work, usually involving multiple custom waterblocks. This website shows one solution for a fanless PC. http://www.zfz.com/