Hello Huang Ray,
It appears that the 250D will accept a Corsair H100i. The radiator dimensions on the H100i are almost identical to the radiator dimensions for our Seidon 240. Our Seidon 240m should fit in the 250D.
As for the other questions, I would suggest contacting Corsair since they are the manufacture of the case.
Respectfully,
Patrick
CMUSA Support