Do you have any concerns that you're creating a trap for detritus etc in the plumbing where it enters the fish room in the garage? I was considering a similar setup as yours, plumbing all my filtration to the garage. I was told it was a bad idea since I was going down (crawl space), then coming back up a few feet when the plumbing got into the garage. In particular I was hoping to do a BeanAnimal overflow, but they didn't think a siphon would ever start over that long of a distance and suggested detritus will build up in the pipes at the garage.
Here's my thread: http://www.reefcentral.com/forums/showthread.php?t=2508545
I looked at your setup. Your drains in the garage are going 50 feet and then going up and entering the sump from the top. My sump will have the drain holes on the side so the water doesnt have to come out of the ground, go up and then in. It will come out of the ground and go directly into the side of the sump.
Also- my sump will be only 6 inches off the ground. The drain in the tank itself is about 6 feet up so lots of pressure. So no, Im not planning on having any issues but all good plans must have a back up and I have one in mind if this becomes an issue.