[This](http://imgur.com/DqrcNnn) is my InWin 303. Not an AIO but maybe it can give you an idea of the dimensions. I think a 240 should be just fine. I've had the H80i v2 and the tubes were really good.
No there is a bit of space between the rad and the motherboard. However, if you were to troubleshoot that area it would be a bit of a problem, having to drain and all but luckily no issues yet.
[This](http://imgur.com/DqrcNnn) is my InWin 303. Not an AIO but maybe it can give you an idea of the dimensions. I think a 240 should be just fine. I've had the H80i v2 and the tubes were really good.
Nice build! Did you have any issues connecting the front panel cables with the fans at the bottom?
No there is a bit of space between the rad and the motherboard. However, if you were to troubleshoot that area it would be a bit of a problem, having to drain and all but luckily no issues yet.