You can't keep bumping your thread up like this in one day. The moderators will tell you that. Sometimes it takes a while for other members to reply to threads. In the meantime, you can do a little searching on your own. Use the search function and tons of things will come up that are related to your question. I think you have some good info already. You will take a chance with losing a fish or having one get harmed, no matter which way you introduce the Red Devils to your tank. If you add one at a time they could fight. If you add them all together they still could fight. A pair may not form very quickly. It could take a few days or weeks for a pair to form. It could also take that long before any major aggression is shown. Many things can happen but the only way to find out is to just try one way or the other. But as suggested before, keep a spare tank ready or be prepared to take some RDs back to the LFS in the case that things don't work out.