>> With arbitrage you also have to beat the fees and the time.
I have to add - coins that you use for trading is also important factor, volatility may lead to situation when you were able to increase volume of some alt-coins, but next day their price severely drops
This is why you need to build a global balancer that withdraws funds into more stable coins once they reach a certain threshold. A minimum (e.g. Max trade size * 3) should be kept in each active coin for trading only.
