In reality you do not need any more oil cooling devices then what already comes on a 400ex. My 440 runs almost the same as a stock 400ex heat wise.
With the extra oil cooler and a oversized oil tank youll need almost another quart of oil "Im guessing" I would start it up and let it run with the standard amount of oil, then add oil till you see a good flow going back into the oil tank.
I know its hard to see but use a light or whatever to try and see if its flowing right, you may need to ditch one of your coolers to get the oil flow working correctly, If you decide to do that I would keep the biggest oil cooler out of the two"IMO" even tho you dont really need it.
FYI = The best aftermarket mod for oil cooling is the spal fan.
400ex hybrid Finished!
http://www.youtube.com/watch?v=YMDIAw8UskQ