FXDD is a company member of one of the top 3 major company in brokerage named Tradition Group, Tradition have presence in 22 countries so it's really big.
About his individual size, I must tell you that his actual capital is around 350,000 USD, some like the 20% more that the minimum required by the NFA but this can be just a strategy from Tradition Group, because for practical purposes, the company is as big as tradition group.
About the possibility to get a trading system i think the answer is yes because they use as one of two offered platforms, the metatrader, so if you program a trade system in mql II, it can be operating by it self, and metatrader offer you the possibility to make back test as well (personally I don't recommend use a automated trading system because all these work fine in dynamic trending markets but force you to give it back in a choppy market) but the possibility is there for you.