I also have a 100g sump on my 300g display. I posted some of my thoughts
Here. There are some pictures of the sump if you read forward a bit. Shameless plug for my thread, but it's a lot easier then retyping what I already wrote.
I really only had a few requirements.
1. Able to hold any water that back siphoned in a power failure.
2. You really do need baffles before the final chamber to trap micro bubbles and contain the evaporation.
3. Flexible. My plans might change.
I think I'd summarize by saying that simple is better. The more complex you get with the design, the more fixed your configuration will be.
- Brad