1. i would assume that its evenly distributed on the bottom around the center, the stator is perfectly center, and the impeller is dead center as well.

2. im not quite sure what your asking here, but im assuming your talking about the flat parts on the multiport bottom on an ek. all they do is mill it
with a square end mill i suppose

3. shouldnt be an issue, but thats some thin plating

4. im assuming those are breathing holes, they go all the way through and arent sealed or blocked by anything

5. probably not, koolance 3/8"ID compressions barely fit