Well my usual advice is not to use a new airport/terminal in the first week of opening. We actually aren't out of that period yet, so I'm not that surprised that they are still having problems. OTOH, I know that some of the problems they have are not quick or easy fixes (the problems with staffing for example), so are likely to drag on for a while. At the same time, for flights by the end of April, I'd probably be willing to risk it - we know when T5 is working, it's working well. When do you need to book the tickets by?