The interviewer asked personal questions in the job interview

Firstly, well done on handling this situation. Many would have handled it a lot worse.

It is inappropriate and actionable to do this, but as you say may be just innocent and naive. If you believe this is the case, perhaps drop the interviewer an email saying "Just letting you know, that some other candidates might have an issue with these questions, as the law in Ireland is pretty clear. Might be an idea to get familiar with the law so you don't have a problem in the future. Thanks for the opportunity."

The only question that is actionable, from what they listed, is the one about the partner.

Questions about what time you get up now are directly relevant for the job. The best answers talk about times (maybe not right now) when you have got up early, and what strategies you used to make sure it was not an issue.

You won't have a business to run for much longer if you keep walking yourself into lawsuits by making hiring decisions on unlawfully discriminatory criteria.

Lawsuit over an interview question? Absolutely - used to happen regularly until employers understood the basics of employment equality legislation. You're not allowed to make hiring/promotion decisions based on the protected grounds - race, ethnicity, gender, sexual orientation, marital or family status, etc. If, in a hiring or or promotion interview, you ask questions about a candidate's marriage, sexual orientation, etc that's prima facie evidence that you are making your decision on prohibited grounds - why else would you be asking about them in the interview? The candidate will have you before an employment tribunal, and will win.

This kind of thing is HR 101. It's frankly not credible in 2023 that you could be running a business that employs people, and be unware of it.

It's got nothing to do with duties of care. You cannot make your hiring decision based on whether they are married or not. Therefore, in the interview, do not ask them whether they are married. This is information which you cannot take into account in your decision; asking the question strongly suggests that you are going to take it into account.

See also: do not ask candidates if they are gay, or whether they have children, or what religion or ethnicity they have. None of these things are relevant to your hiring decision, and making a hiring decision based on any of them will leave you open to legal action.

I've already explained this, your countship. Read the next bit carefully, and try to grasp it as you go. By asking the question, you hand the candidate evidence strongly suggesting that you intend to make a hiring decision on one of the prohibited grounds. This will considerably strengthen the candidate's case when, in due course, they take you to the employment tribunal alleging that you discriminated against them on one of the prohibited grounds.

If your concept of "developing a robust nature in tackling nonsense" embraces losing actions in the employment tribunal because you provide evidence against yourself, and paying out substantial compensation as a result, by all means continue to ask the question.

Once upon a time I'd have asked personal questions about family etc at interviews, but I'd only have done it to help put the person at ease and try to forge some kind of a connection. If you can do that you have a better chance of finding out what the person is like.

Of course it can't be done now and that interviewer is totally out of order. The reasons why they are out of order are less important, even if it is seen as alright in their own country it just isn't here.

Sorry it didn't work out for you OP, how you get a job you like soon.