Sump planning

[target]

Hi All,

I am getting ready to start a new tank, a 180g, and wanted to get thoughts on my sump design. For the sump I bought a 48x18x20 tank. The chambers from left to right are the drain/skimmer (9.6g), return (9.75g), fuge (13.25g), and ATO reservoir (10g). Total used: 32.6, not counting the ATO. Total available in the sump, not counting ATO would be 53.8g, leaving me with 21.2g of overflow space in the event of a shut down. I've not had a tank this big before. Does that seem like enough room? or would it be better to get a seperate tank for the ATO and use the additional 10g in the sump?