Looking to pay someone to double check my schematic and lay out the board.
We can do that -- send us e-mail at support@ruggedcircuits.com
Optionally depending on manufacturing cost I may combine this with the 2560 into a single board. Thoughts on that?
It very much depends upon how many units you want to build. If you want to build just one, you will spend more design time integrating the ATmega2560 design and yours and it's cheaper to just piggyback onto a Mega. If you're planning on building 100 then it will be definitely cheaper to design and build an all-in-one board rather than buying 100 Mega's and designing/manufacturing 100 custom boards.
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The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected