Maybe you should look at MultiCharts as an option. It's very similar to TradeStation and most code written for TradeStation can run in MultiCharts. I researched both before going with MultiCharts. The main advantage with MC is you get to pick your broker from a list of brokers that they partner with. One disadvantage is paying for a separate data feed but from my research a lot of people complain about TradeStation data. I went with IQFeed for data and its working great.

Since you're not in the US you could pick a non-US broker or one with overseas operations (Interactive Brokers has this) and be able to trade the long/short strategy you speak of. I definitely understand the logic behind what you're trying to accomplish. Here in the US you'd have to have 2 separate accounts to pull that off. Running a strategy like that with 2 or more accounts may not be a bad idea since you'd be able to evaluate the performance of each strategy based on the performance of each specific account (something to think about). Hope this helps a little...