Just a quick point - you say that the IR is "on a twin". Doesn't have to be. Obviously you need it on a twin before you can apply for the airlines. But if you plan on, say, instructing for a couple of years before applying to the airlines, you can do the IR on a single. The advantage is that I'd imagine it's easier, it's certainly cheaper, and you're very unlikely to be able to keep a twin rating current, IR or not, if you're doing PPL instructing. But as long as you get an IR within 3 years of the exams, and renew it at least every 7 years thereafter, your ATPL exam credits are still valid, whether the IR is on a single or a multi.
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