A lot of it is dependent on money. The family had the 300 gallon DD set up as a reef at one point and we had a bubble king skimmer on it. Was very expensive we picked it up used for $1500 at the time. A 75 gallon sump is a good size personally I would go with a 125 or 110 6ft as it will add more options for your filtration and you will enjoy the added room. You can make a frag section in the sump. For a pump, a lot of people like hammerhead/barracuda and blue line pumps, again, personally,I have no complaints about the jebao series DC pumps. You can usually pick up 2 for the same price as one of any other pump. For circulation I would go with 2 mp40s In the upper water column both with battery backup. Maybe 3/4” up the tank. Then I would place one of the cheap amazon koralia knock offs right in the centre of the tank on the back wall with the outlets angled to the side. I bought the 3200gph ones and had no complaints about them, they can be angled (aimed) wherever you need flow. This will give a good circulation pattern in the larger tank