Like others have said, you want the siphon and open channel to be about an inch below the water surface in the sump. If you go too deep, it makes it harder for the system to purge. I have personally set one up like that in the last few weeks. It took me about an hour to figure out why it just wouldn't purge. Even at 1200 GPH, it just didn't have enough velocity to push the air down against the 6" of water above the pipe exit. 4 inches may be OK, but personally, I would cut the pipe off shorter so that it sits just a little below the surface. At the very least, it will make the system purge faster. The open channel depth doesn't really matter, you can leave it at 4 inches and it won't make a difference. I would leave the siphon line at 1" all the way. The open channel and emergency may benefit from increasing the piping size to 1.5". They should handle the flow easily at 1", however, they will handle more flow silently at 1.5", so it doesn't have to be as perfectly tuned. Preferably, you would want the gate valve closer to the sump. By putting it at the bottom, it usually allows the system to purge faster as well.
You want the siphon line to be low in the external drain box. The open channel is what actually sets the height of the water level in the external box, so adjust accordingly. Finally, you want the emergency line to be a straight pipe that is atleast 1.5" below the very top of the box. I'm not sure how tall the box is, so you may have to test and tune it to make it perfect. All of these things may not make or break the system. But using some "best practices" will make sure that everything runs with as little chance to a spill as possible. If set up right, it should purge in about 10 seconds and not require any intervention during restarting.