They do come in two sizes though (of course not in commonality), the 717 is a downsized MD90. They do lack the 160-170 pax layout of the A321 and 737-800, but I usually fly them in a 134Y/4-8C pax layout which is ideal from operating from large hubs to smaller airports. I might miss out one the 30+ pax profits, but it allows for a higher L/F even if competitors encroach. And since you get them first, you can always replace them when the 737 NGs arrive (for DXB the extra 5-800miles range makes a huge difference, so the A320 family is counted out). I have about 90 737s, 30 738s, and 15 736s arriving in the next three years.
As to routes schedules, I usually schedule only one per plane 1600-2400 first leg - 1600-800 second leg (A-B-C-B-A legs), and this usually means that they fly about 75% of the time (leave lets say at 6 and arrive at 0400). Because of A checks I sometimes have to move my Saturday flights a bit earlier. With the 737s a 2800+600 approach works the same way. This allows me to get more pax demand then I would be able to get just from my hub (more potential for growth), about 40% of the pax numbers I get, I get from the B-C-B legs.