Welcome to the forum
1.) No idea because I have no clue what 3/8" means in millimeter.
2.) you should write an email to
support@aqua-computer.de because nobody here in the forum can answer this.
3.) I recommend a airplex evo 240 or 360 with fans. This is much cheaper and has enough reserves to cool down a high end system. With a small controlling unit you could adjust the fans to your needs: pure colling-power, silence or just the good old middle course.
4.) that's no problem. Every cooling block is tested with a very high pressure before it is sold. Your pump would be the first pump ever which is able to crack this cooling block ;D
Also keep in mind that the real flowrate of your pump is much lower.
5.) you can use a twinplex with the chipset mounting but there is a little problem: a capacitor is blocking the mounting. A lot of users just solved this problem like
this or
that :
6.) if you use a block like the large aquadrive you are able to reduce the noise of your harddisk(s). If you do so, you have to take care that your watertemperature is low enough, because otherwise you would heat them instead of cooling them.
7.) for your graphic card you can use a twinplex (pro) in combination with passive coolers for the RAM. Or you buy a aquagrafx block which cools GPU and RAM.