Ok I'm not going to argue the points that have been made, some are good-some maybe not so good.
If this was me,
1. I can't think for a minute that ordering 10 fish all at once is a good idea. I understand the want to introduce them at the same time but what a handful.
2. I sure wouldn't put them all in the same tank. The entire idea of QT is to QUARANTINE. What exactly would you be quarantining by placing them all in 1 tank? All you are doing is keeping the fish in your display safe, while placing all the new already stressed fish into jeopardy. All it takes is for 1 of those fish to be sick and BAM they are all dead. That's why you are attempting to quarantine right? So that they all have a fair chance at living. I could understand placing them all in a quarantine together if they were all suffering from the same situation, disease, parasite etc. Right now you need to quarantine them from each other as you don't know which 1 might be the time bomb.
3. I certainly would not use 100% water from my display tank. That water is dirty. I always like to go back to the beginning, why are you doing the water change? Because you've deemed it unfit for the display tank and inhabitants. How on Earth does that translate to "perfect for already stressed fish". Just like your display, dilute the old nasty water. I'm certainly for using some of it, maybe 70% new to 30% old. That way you get some of the benefits of possible bacteria and such. Yet if I was investing in thousand dollar fishes, and yes I once had a Blue eyed plectostomus that retails around $4-5,000 each, I think that I would be mixing up a perfectly matched batch of new water. That way I could be 100% certain that no creepy crawlies would be in my water at all. I'd be matching the important things like PH, SG, and ALK. I'm certain I wouldn't be worried what my calcium levels would be.
4. On to keeping the fishes in separate tanks. Not knowing how large the fish are that you are ordering. I'd probably be looking at 10g tanks for fish that are around 3-5". I'd decorate with sterile items such as pvc or broken clay pots. The reason for small tanks is that I'd be doing daily water changes of at least 50%. The smaller the tank, the easier that is. I'd try to have a very large container of pre-made water so that it is always consistent. With a smaller tank I'd only feel the need to run some sort of cheap filter with carbon in it. Probably a sponge type filter that I could load with bacteria. No sand, no live rock. I'd also run a smaller tank so that I could use less medication should the need arise to treat 1 fish. By using separate tanks only the fish that needs attention gets attention, thus reducing possible stresses on otherwise "healthy" fish. A smaller tank allows me to quickly remove the water to alter the dose or to do 100% water changes and then continue my medication dosing so that I know how much is in the water. Kind of like water changes, as you keep adding meds we don't know what it is doing to the water. By removing the water and replacing it and then reapplying the medications, we control exactly how much is in the water. Live rock and sand can allow microorganisms that could be bad a place to hide out. Once hit with meds it could be totally useless on the "beneficial" scale so worry about it.
5. I think I would be watching them and worrying for about 2 weeks. After that I'd become a little more relaxed and begin doing smaller and less frequent water changes, slowly building them up. After about 4 weeks, and showing no signs of issues, I'd begin to slowly add more display tank water during my water changes. After about 5 1/2 weeks I'd have them in about a 80% DT water to 20% new water. That way they could be considered "acclimated".
6. Maybe around week 5 I'd consider allowing them all together in the 75g to see what challenges arise before adding them to the DT. But then again, the tank is much smaller than the DT. Those that may fight in the 75g might not quarrel in the much larger DT. Personally I think I'd first pick the less feisty fish in the DT for a couple of days to find shelter. Maybe the first 5 fish. I'd probably want to wait 2 weeks before adding the rest. I think the general consensus on the "safe zone" is 6 weeks for a true quarantine period.
When I first got in the hobby 1 great piece of advice I received was to treat each new addition of fish or such livestock, as a huge bio-reaction. Your tank will stabilize to the new addition by colonizing more bacteria and such. Typically your tank only has "X" amount of bio-filtration taking place. For each addition the tank will need to ramp up to catch up or it can become polluted as the filtration lags behind. So I kind of heeded to the 1 fish per 3 weeks. Basically allow the tank to mini cycle between fish. Of course that becomes difficult with territorial additions and schooling type fish. That's why I mention to break it up a bit, add some fish and watch the parameters. Let the tank settle down and then add the rest. Make sure your skimmer can handle the new pressure, watch for algae, watch your nitrates to see if they rise. If the trates rise, really watch the Ammonia and Nitrites as of course most of us know, they kill fish quickly. If they rise, I'd think water changes would be the most efficient way to bring them down. I've never used a bacteria supplement, however I'd get opinions as it would seem that dosing the display a few times before the addition of fish might be a good idea to kind of boost the tanks immunity.
So that's my take on the situation. What may be good for me, might be the complete opposite for someone else.