imo it's a very vague set of questions..what do you mean by "system"? do you have the rules and stats already and just need some automation? do you know programming? how well? in 15 years old tradestation 2000 you can "develop" system just by clicking on set of rules. won't get you anywhere,but hey..that was an option. will it work for you? how would i know...on other hand-you can develop automated system in excel too. https://www.tradestation.com/~/medi...ing/Books/Designing and Using Strategies.ashx
For the Cooltrade price of $3500 a year you could hire a programmer to set up an interface to Excel and own it as opposed to rent it.