Building an External WC Box...

I got my pump late last week and now I need to put something together to house it in. I had always planned on making this an external setup, so I've decided to build an external box for it, but have a couple of questions.

1) With the heater core being on one side and the fans on the other blowing out, is there an optimal distance between the two?

2) This box will be sitting on a shelf next to my computer, so the width of the box is limited, so I will have to put one part on top of the other. I read before that the reservoir should be at the highest point... is this correct or would it be ok to put the heater core on top and the pump/res underneath?

Here is what's going into my system...

CPU Water Block - Cascade
Heater Core - Fedco # 2-342
Pump - Swiftech MCP 600
Fans - 2 Delta 130 CFM controlled by a fanbus
Reservoir - Criticool WaterPlant
Tubing - ClearFlex 60 1/2"

My box will consist of two parts, one for the heater core & fans and the other for the pump & reservoir.

it would be fine to have the res below everything i think.