WtksBlondie104,
I'm sorry to hear about what is happening with your fish. I hope that he can pull through for you. I also understand your frusteration of needing help and not getting clear answers. I hope that you can understand that no one wants to take a stab at what is happening unless they can lead you down a path they feel will help you out.
When I first started posting to this forum I was making several mistakes that made it hard for someone to respond to what was happening. Until people get to know what your set up is then try to include it in your posts. Even if it seems redundant. I get the best response when I list everything. Don't worry about taking up too much space. The more info the better. Simple things like where your levels are at, what's in the tank, how old the set up is and even things like lighting. This will help get some ideas and a possible answer to your problems.
Now for some tips that may help for things that you've asked. Unless you are doing a fish only type tank I recommend that you keep all fish that you get in a QT tank until you feel confident to move it to your display tank. Some people wait two weeks others as long as six weeks or more. Depending on what is happening with the fish. In your QT tank only place a few things like a pvc pipe or a piece of lace rock for them to hide behind. Try to keep it as bare as you can stand. The least amount of stuff in the tank the better. If you are going to use this as a true QT tank don't put things like LR in the tank. You won't be able to use most medications to treat anything if you do.
As far as being able to keep your tang. It is possible. I know the frustration of the one unobtainable fish that you so want. Any fish I name dies so I no longer name them out of fear of losing them. If you take what others have suggested and QT him first there should be no reason that you can't be a proud parent to a lovely tang. The thing you have to remember is that for some reason tangs are ich magnets. I haven't seen any that don't show with ich during transportation from the LFS to your tank. Copper is a great medication that kills the ich. Unfortunately in a reef setting it also kills other things including the LR.
I know many of these people now here at CR. They all want and will help so try to know that no one was ignoring your please for help. Please keep us posted on your progress and know that many are pulling for you even though they don't know you. Many will be glad to spend hours helping you get the set up you want and help you with even the basic of questions. I hope I haven't rambled too long for you and that this will in some way help.
Angie