add a oil cooler a good idea? and coolant leval queston.

[getdrunk]

im thinking of adding a 400ex stock oil cooler to my yz426 oil lines or maby put 2 oil coolers on it 1 for each line. good idea?

and for the coolent how much do i put in it? ill have a 250r quad radiator on the yz426 and no white bottol thingy. i heard that you can put to much in and it will wear out the water pump fast so how much do i put in?