To answer the original question, ich can still show up if you only QT for 2 weeks because this is not a long enough QT. However, if you QT for 3 to 4, you have a much better chance of keeping an ich free tank. Ich needs to be brought into yoru tank for your fish to come down with it. If you QT and hypo all of your fish, the chances of you getting ich in your main tank is extremely slim to none. I say slim because anything can happen, but general speaking, hypo and QTing all of your fish is the best way to ensure an ich free display tank. Picking healthy specimens is a very good way as well. If you watch a fish eat the the LFS, your chances of that fish being healthy and disease-free are much better than if you don't watch it eat before you take it home.
Raising your temperature to 80 degrees will not really do anything as far as ich. To speed up the life cycle of ich, the temp has to go to about 85 or 86 degrees at least. This is not very healthy for fish. Furthermore, it is best to avoid fluctuating your water temp and salinity when possible. This only further stressed the fish.
Next, lowering the salinity to 1.018 is not a good idea either. This too will not really kill ich, and will have a drastic effect on your inverts, and eventually on your fish as well. This is way too low for inverts. Usually, 1.021 is too low for inverts. 1.018 is very bad for them. Fish that are kept at lower than natural salinities also live a shorter life as well. This has been proven.
Also, if you cannot catch all the fish in your tank and you have a bad outbreak of ich that you need to get rid of, QTing some of them will not do the trick. You need to get all of them out and QT all of them, or else you will not rid the display tank of the parasite. In ridding the display tank of ich, you need to hypo all fish that the parasite could possibly live off of, and then let your display run fallow for 4 to 6 weeks. QTing the ones you can catch and medicating the others with a reef safe med like Kick Ich is pointless. It is a lot of work for nothing if you ask me. If you are just going to do that, you might as well leave all the fish in the tank. Using a product like Kick Ich does not guarantee that ich is going to be killed.
I do agree to avoid copper though.