U shape flow path will give you more evenly distributed temperature, (less hot spot) however your flow may reduce by 1/6~1/4 depends on your inner design. Though I would try very hard to avoid inlet and outlet coming to base with 90 degree bends, maybe a little tilted entry and exit angle?
If your pump has plenty of head and spit out 100+L/Hr when no load, you should be pretty good shape. Just find a low resistance rad that fits two 120mm fans and you can easily handle 3~400W of heat.
Designing WB with less than 36L/hr flow would be a pain in the butt, specially total mass of WB and connecter (no liquid) is not allow to break 400g...
