Here is a picture of my sump. The notable things are:
1. Inexpensive - Made from and old 30 gallon tank I had. I know it isn't pretty.
2. Two Acrylic baffles siliconed in place creating 3 sections.
3. There are pvc bulk heads at the bottom of each baffle. This allows me to insert different length stand pipes to change the water level in the 1st two sections.
4. I have ample room in section 2 and 3 to contain the draining water from above when the return is switched off.
5. It's hard to see but my water level in section 3 is the lowest and this is where the return pump is. If for some reason the overflow stops working, this is all of the water that can be pumped up to the tank, and I have sufficient volume left in the tank that this will not flood over the sides.