Here are the things I would do different about my sump if I were doing it again, hopefully some of these might help you. 
 
First you want as much directly overflowed water as possible to go right into your skimmer pump intake.  A corner acrylic box in the sump, or even a small plastic container with a hole in in for the pump intake, will do this. 
 
The deep sand bed will be easier to maintain if it is in a removeable bucket.  It is hard to siphon stuff out of a sump at floor level. 
 
I wouldn't grow Xenia or anything else in the skimmer compartment.  You want the skimmer are to be clean, you don't want anything to foul the skimmer pump intake. 
 
I would allow more room than is needed for the skimmer.  My skimmer barely fits in my sump so it is pain to remove it for cleaning. 
 
I would suggest a modification to the standard baffle design.  To most efficiently remove air bubbles with a baffle system, you want the up-flowing water to go fast, and the downflowing water to go slow.  A narrow spacing between baffles where the water goes up, and a wide baffle spacing where the water goes down, will accomplish this. 
		
	
		
		
		
		
		
	
		
			
			
			
			
				 
			
			
			
			
			
			
				
			
			
		 
		
	
	
	 |