You might find this entertaining...I thought our builds were headed toward identical until your rockwork went over the entire wall! Looks good.
http://www.canreef.com/vbulletin/showthread.php?t=28436
My $.02...I've had a lot of trouble getting the threaded fittings on the OM 4 ways to seal nicely. I have lots of threaded joints. The only one's I'm having trouble with are the OM 4 ways.
I'm concerned that three darts isn't enough flow...it looks like I'll find out before you!