I’ve numbered the questions for ease of answering…
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If you keep the option set to this, as Jaxs pointed out, then yes, they will. However, it will first use up any flight crew you might still have, so no, you won’t have a surplus if you keep ordering more of the same type of planes.
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That’s a matter of weighing cost against benefit. If you think you can earn more with the current cabin than with the one you have in mind to use in the future, and in fact earn enough to cover the cost of replacing the cabin interior, then you may want to hang on to this one until bookings start to drop off. Be aware that this may have a slight impact on your image, though probably nothing alarming.