thoughts on closed loop system

I guess that depends on what you are wanting to do. An intake and a couple returns in the back wall is easy enough to plumb now and shut off with valves and caps. If you want a complex closed loop with several intakes, and returns all over the place that will be a little bit more work, and a lot more money in plumbing, especially valves. Its going to be harder to make changes down the road when you can afford the equipment you are wanting. Swapping plumbing and making changes while the system is up and running can be a real ***** if it wasn't planned out correctly from the get go. Plan with the end goal in mind, and make sure you can make changes and upgrades to the closed loop without too much hassle, such as draining the entire tank.
If that sounds like too much of a hassle, and a disaster waiting to happen then ditch the closed loop idea and get your flow from internal powerheads.