100 Gal Tank setup question

[AceZ28]

Ok I am working on setting up a 100 gal saltwater tank. The real question i have is I am wondering if the drainage hole is big enough. In the back of the tank in the very bottom it has a 1/2" hole. I talked to some of the places that make saltwater tanks and they say I might be able to make it work but they say that I prolly wont be turning over enough water. So i want to get some other peoples opinion. The return pump is going to be a Rio 2100 which with the length of tubing it is going to have the box says it will move about 350 gallons an hour. Plus I want to make sure that i dont flood the 100 gal by pumping to much water from the sump. The sump is going to be a 20 gallon tank that I will put dividers in to make the water flow or do yall think that it would be a problem to leave the 20 gal as it is and just have a hang on filter. I have a 30" US Acryllic??? protein skimmer also. Any suggestions will help greatly.