There are many different types of sumps that try to accomplish different objectives. I think you need to spend more time researching sumps and the various types here on rc and in other places on the internet. I think the research will help you make a better decision as to what you want to accomplish for your setup. There are high flow and low flow sumps. There are sumps that use plenums, reactors, probe holders, ato devices, refugiums, skimmer sections, algae scrubber sections, sumps that have holding sections that can be isolated from the system for treating sick fish or coral. The point is that a lot of things can be integrated into a sump or it can very simple. I think the best thing for you is to educate yourself immensely on sumps and see what others have done and figure out what you want in a sump. You need to look at all of your equipment and decide what will go in the sump and what will stay in the DT. You said you had a HOB skimmer, they need to have a certain water height to operate correctly and if you change the height of the pump or lower it in the sump it could change the efficiency of the skimmer when you put it in the sump. Sumps can use HOB skimmers but generally use in sump or external mounted skimmers. So there is a lot to think about. There is a lot for you to educate yourself on. But if there is any bit of advice that you must adhere to is this: when your tank looses power and you are using a siphon for water to leave you DT and go to the sump, the water will continue to leave the DT and enter the sump until the syphon is broken. You need to plan on this happening and allow room in the ump for this to happen. Design what ever sump you want and include what ever equipment you want. Heck design it with a UPS back up system so that when the power goes out you have back up power. BUT always design the system to allow for the power to go out and a certain amount of water to leave the DT and enter the sump. Its inevitable and this one point will save you a flood from a power outage, it will not save you from a leak from a tank or sump. Some things you can plan for and some things you cant. Good luck with this endeavor.
