With short run lengths like that on the ground side, you can run a much thinner cable than 1/0, like 4 or even 8 ga. It can be mathematically calculated but I can't tell you the formula off the top of my head. A thicker cable wont hurt you though except for the added weight. Do a voltage drop test on both the ground and positive cables with the engine cranking. To do that, measure with a volt meter from the positive battery terminal to the positive terminal on the starter. Then also from the negative terminal on the battery to the engine block. If you get a reading more than 0.1-0.2 volts, the wire is either too thin or the connections are dirty, have paint on them, etc. The idea is to have as thin a wire as you can without any voltage drop, with maybe 1 wire gauge thicker for comfort. Since the most current is flowing when the engine is cranking, that's when you want to do this test and the test will only work when current is actually flowing. Here's a handy little chart I found when Google-ing wire sizes too:
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