I'm going to summarize your questions for you:
1) How many quarantine tanks should I have?
One for the new fish coming in. If they're coming from the same LFS, they are already still probably sharing the same water. You need to be sure for any quarantine system that you set up that you have accurate temperature control and filtration. Keeping a good quarantine system is hard. So hard that a lot of advanced reefers who have been in the hobby a VERY long time have said, "I just get a new fish and throw it in and hope for the best."
2) Can you move the old fish and the new fish into the new tank on the same day?
Yes, if it's very well cycled and probably if you're done something like NoPox to help feed the bacteria populations. Without fish to produce waste to feed the bacteria, it's going to be hard to grow enough of it to handle the fish load. Especially depending on how many fish you add.
So no, you can't add them on the day that it's set up unless you are 100% sure that you have very establish live rock. Even then, I would say your chance of success and of having a well tested system with no leaks is very hard. Also, setting up a 300 gallon system takes more than a day even if you have a lot of experience. That's a fair amount of plumbing work, rockscaping, lighting setup, temperature control. It's complicated. And, how do you intend to make 300+ gallons of salt water all in one day? It took two days to fill my tank with RODI water, and you don't want to dump salt in and then dump fish in right away.
3) So I put my current fish into a quarantine system?
You'd be better off moving your existing system. If it's sumpless and a 135, you could probably get enough people to drain most of the water out into bins and then push it out of the way, then carefully put the water back in.
4) Should I set up 3 40G breeders as quarantine tanks?
That would be extremely difficult to maintain and temperature control.
5) Do I treat fish from my LFS that quarantines them for two weeks?
Quarantine procedure is really an individual thing. Nobody can answer that question for you. I watched a long video on success rates with different butterfly fish. They rated them in categories and the best success rates were, if I remember correctly, >40%. Some of the fish that you're trying to keep probably have a 50% chance of surviving past the first 90 days if they have ideal conditions and great food. Your chance of being able to maintain a quarantine system perfectly for a long period of time is slim. Their best chance is possibly to put them all into the new cycled display system as soon as it's for-sure ready. I would decide that it was for-sure ready when you can test the tank for a couple of days with high quality test kits and see no ammonia or nitrite after a pretty heavy feeding of frozen mysis into an otherwise empty tank.
6) Does copper expire?
I have no idea.
7) I've seen people with tons of fish. How do they do it?
Most people just keep adding more. I got the majority of the fish in my system from the LFS on the same day and put them in with about 5 other fish. I only lost one clown tang that was too thin when I bought him (mistake on my part,) and if you add enough at once, especially to a large tank, it disperses aggression. Adding one or two fish at a time can be tricky, but people do that, too.
Note a lot of fish are very hard to quarantine because they are better off with pods and algae and stuff that grows in your display tank but not in your quarantine tank in order to survive.
Also, each fish will have its own personality. It's nearly impossible to predict what a fish is going to do.
8) Does anybody use Bubble Magnus?
Yes, people do. There aren't a lot of good scientific comparison tests between different skimmers. The only one I saw was maybe 7 years ago and it said that there was little difference between skimmer performance as long as they had similar air draws. I went with a very old, massive GEO skimmer with a huge pump and it's working great for me. It was in a "garage sale" at a LFS for $20 without a pump. I like it.
9) How do I keep a lot of anthias?
Luck, lots of food, an established system, and I'm finding mine love live black worms.
10) Should I get angels?
Depends on what coral you are going to have an whether you care if it gets nipped at.
11) Why is rock going to die off if moved to a new tank?
It won't, but you won't have enough rock, and you're adding a lot more fish. It's complicated.
12) If I get 2 anthias and add others later.. ?
Yeah, don't do that.
As previously stated, the large reef forum is really for advanced system design or build threads. When I clicked on this thread, I was not expecting this. I decided to take a half hour and try to answer all of your questions for you, but these are all beginner questions. You have never successfully had a sump before, you're unsure what skimmer to get, and you aren't sure how to add fish to a system. You've also lost a couple of fish after five years for unknown reasons in an established sumpless fish only system.
You also don't have any information about the tank that you're having built other than that it will be drilled and that it's going to have a skimmer. You have a lot more choices to make. Lighting, reactors, controller, heaters, fans/chiller, water movement in the tank, overflow style (herbie is awesome), return pump selection. Claim to be very experienced if you already have all of that planned out, but if you do, the thread doesn't indicate that you do. I think a lot of people are resistant to answering your questions because it's a rabbit hole and they don't want to design your whole system for you.
