My new tank has less than 1/2" of sand and it will be vacuumed with every water change. Previous tanks had anywhere from 2 to 4 inches of sand and they were all stinky and disgusting when the tanks were moved. I did the DSB and every time at about the 5 year point problems from waste in the sand reared it's ugly head.
3 to 4 inches a good amount and 6 inches or higher considered DSB. I would use the 4 inch amount though.
Also you dont want to vacuum your sand as you will be removing many wanted critters.
Also feeding flakes fine but mixing it up much better. I feed flakes in the morning only what they can eat in 1 or 2 minutes and then feed frozen in the evening only what the can eat in 1 or 2 minutes. This reduces uneatin food and excess fish waste collecting.
The best thing is good high water flow which increases good gas exchange at the surface and also increases the use of your best bio filters the LR and SB by pushing water through them.
Not to sound mean but you sound un informed and i would research this difficult hobby more. It may seem easy for a few months or even a year but can go wrong fast and hard.
That assumes live sand with the associated critters was used to establish the sand bed. My choice has been to bypass the live sand with the associated critters and vac the sand bed. After doing the DSB and Live sand bed I think vacuuming the substrate is a viable option.
Perhaps it could be a visible option but it also bypasses the reason it needs cleaning. With proper water flow and CUC with a good maintenance routine schedule vacuuming would not be needed . Yes , No . either way i have never needed this myself.
With all due respect to DR Foster and Smith, they're in the business of selling sand. I just bought a 40 pound bag of Seaflor Special Grade , used it in three tanks (Total volume 45 gallons) and have ten pounds left over.