I'm afraid there simply isn't an answer.
You can't estimate the resource usage of any complex system like these because the answer depends on how you use them, how you configure them, your surrounding infrastructure and so-on
I completely understand why you are asking and have every sympathy, because I've been there many times myself. It's really hard and quite frustrating to have to sit there and say "I really don't know" in any talk about resources.
Unless you can say "we will have the same usage pattern as existing system that belongs to X", there's no useful answer. 1 CPU core per 10 users is too simple a formula, because it has only one factor and that's not enough. Even if it were a valid starting point, before it can tell you anything, you have to combine it with information on the nmber of issues those 10 users are going to filter on, across how many projects, with how many custom fields to search and/or display, and... and... and...
Random example - one place I worked had 20,000 users and were running Jira fine on Server X. My current main client has 6000 users and virtually identical hardware and are moving to more CPUs because they're struggling. It's just not a simple question.
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