a couple things i'd like to add if i may-
1. nothing in the sump needs dwell time. as long as your skimmer, macroalgae, heaters, and reactors if any, are touching water, they will work efficiently.
it's a mistake to have too little flow in the sump however.
2. drilling is very easy, and it's completely untrue that an older tank will crack easier than a newer tank. on the contrary, many newer tanks are completely tempered, and are unable to be drilled.
3. drilling a tank is much better than using a HOB
overflow. bulkheads can leak, but rarely do when installed correctly, and when they do, it will take a very, very, very, long time for one to leak down to the drill hole. if you don't see it leaking way before this, you are one of the least perceptive people i have heard of, and chances are, this tank will not do well.
overflows can fail to restart after a power outage. in this case, the return pump will overflow the display until the sump runs dry. this can happen in 30 seconds, and can easily be missed. even if you choose a CPR overflow which utilizes an aqualifter pump to start the siphon, there is a margin of error. those aqualifter pumps wear out in about a year, and you won't know it's not pulling until one day when you need it.