As you already have the pumps, closed loops may be fine for now. They addition of the 4MD on a closed loop should generate decent current. I had one that was not drilled. Just a "U" pipe over the top, with a slotted down pipe intake. The return also went over the top. Drilling is neater though. Later on you could purchase the larger 6110 controlled, pulsing stream pump and run in on one end along with a closed loop.
I think you will be fine with your plans for now.
You could also do as I did. Sell my Mak4 pumps to buy Tunze,s.
