sump question

[chadryman]

I have two questions;

1. The sump on my 26 gallon bow front is about 18'' long, 8" wide and 12" deep. It looks like it would hold about 10 gallons or so filled to the top. I also have a 500gph pump and airstone protein skimmer. How much larger of an aquarium could get if I wanted to keep using this equipment and still have a healthy reef?

2. I also want to start a small 10 gal. set up for mantis shrimp. What kind of filtration do I need for something like that?