I just think you are diffusing the flow too much. You have the right idea though. I think it you just stuck with two outlets for your closed loop you will be fine, that tank is not that large, so I don't think you need four outlets.
I do like the idea of the flow returning from the front however. It is hard to ensure all the corals get good flow from that angle. That is why I like sea swirls even though they do cost a lot for what they do. You also might want to consider a spray bar manifold to go across the front with a smaller closed loop pump in additio to what you already have.
Flow is a very difficult issue to deal with and honestly it is always difficult to say if you have enough flow until you actually put the setup into action and have yur rock and coral in there.
As your corals grow you will find your flows need will change as well.
sorry no concrete answer
Mike