ok, you've got a blank check. the firm says go buy a front-end and tweak the rest. what do you buy to trade fx, futures, equities, and bonds? what particular specs of an API would be key for u? what would keep latency lower?
essentials for development. big multiple monitors, fast computer, linux, quiet, good chair for API go with http://www.aegisoft.com/ and start development in c# or java even though the clueless will rant you have to do it in c++. dont write everything yourself, grab libraries from other places.
TickZOOM has extremely low latency and unlike most data engines can handle the bandwidth of tick with 5 levels of streaming DOM data. It generates any combination bar data on the fly so you all you have to write is your strategy. It will be released to beta around the end of the year. Wayne