Alright, i can speak about this with SUPER EXPERIENCE
I had a Sand Sifting Star (assuming thats what sss is?) and went ahead and added a diamond goby and they both did awesome for a few months. However, MAKE SURE, again, MAKE SURE!!, that you have the top covered, expecially with something like damsels, because they spook easily and when that happens they LOVE to jump, I lost 3 of them, made it through eggcrate AND a double layer of pond screen with a screening kit, they are awesome at 2 things, keeping an immaculate sand bed, and ending up on carpets
About getting rid of the damsels, they may be pretty but ultimately will restrict anything else you can get really. They are very mean little fish, and there are much better choices out there for fish choices, so I would vote yes to getting rid of them. I do like the names though, very appropriate.
At first when the goby is added everything will get covered, especially with a small sand grain size, but eventually once it has went over everything about twice the sand stops covering everything, whether it be all the really small stuff gets filtered out I dont know, but I noticed a huge decrease in the amount of stuff which got covered after about week 2.