Will this work?
In principle, yes.
What problems do you see?
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Availability of 4oz PCB, but you may have someone who will plate up to that;
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Stability of 4oz PCB if you can obtain it (making it flat an keeping it flat could be an issue on FR4);
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Switching losses with a simplistic gate drive; and
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The ease of causing fire or explosion when handling currents this big! Especially when commissioning the gate drive PWM functions ]:D.
suggestions to improve it?
a. Consider single-sided aluminium substrate PCB material for the MOSFET stage, like http://www.bergquistcompany.com/thermal_substrates/t-clad-product-overview.htm. I can connect you with a UK PCB manufacturer who specialises in this, but you may find one in NL;
b. If you have 12V available in your system, consider an active gate drive circuit, either using discrete transistors or an integrated bottom-switch driver. I'm using the UCC27533 on my current project, (see http://www.farnell.com/datasheets/1712835.pdf); and
c. Consider a high-speed over-current protection circuit, with a low-value sense resistor between source and Gnd and a comparator to sense an excessive voltage drop. I'm not so familiar with the MEGA family, but on the XMEGA I configure either in-chip fault protection functions, or events (faster versions of interrupts), to shut off the gate drive if the source current exceeds a safe limit.