danger, I don't think that the CX API can be accessed by anyone but a white label provider. Now you may be able to access Gains API and get it to talk to CX, but direct access, I really don't think so.
Don't forget, all preset orders on the CX, and Hots are synthetic resting orders. In other words when the price is hit they convert to market orders, so there is no guarantee that the order will fill anywhere near where the order is placed.
Obviously this is hard to program, how much slippage I mean.
We work through a White Label provider on the CX, this means the we do not get access to the API. Now would it be nice to be a white label provider and get direct access, yes, but that means biiiiig bucks and heavy duty relationships with several banks and others to be our counter parties. I am ok as we are but who knows what the future will bring, because our principles have the bling.
The closest I have found so far for this kind of trading is MBT, although Steve don't like de VIPER, but the platform is very flexible. It also works with tickquest, and you can design and build strategies with them. I use Tickquest by the way, and don't get a discount on for mentioning them here

. I don't know how their liquidity is, how the fees and spreads would affect your system. And I have heard of some outages on the servers but I don't know how many times this happens.
So you might want to check them out, I am sure they will compete fee wise.
The Ever Trying To Assist VIPER