Hi,
Yes, that approach sounds very reasonable! As these are three very different (and often complex) tasks, it definitely makes sense to run then in sequence, to allow annotators to focus on one specific task at the time.
Just as a little tip: When you start off with your project, I would start by annotating a small portion of your corpus with all three tasks first. This will help you see whether your annotation guidelines of the first steps support the annotations you want to make in the last steps. You don't want to go and annotate all your corpus with NER, just to figure out that for REL or EL you should have done the NER slightly differently.