Juggling multiple job applications

I think you're jumping the mark a little. There's nothing you really can do until you see if you have a clash of dates, Then you can reschedule or prioritize.

Edit: On re- reading it appears you are expecting to get more than one offer.

That's a fair spread. You're basically talking about, say a 40k salary vs. a 100k salary. If you are realistically, or even aspirationally, hoping to be considered for a 100k salary, why would you even consider the 40k one?

Of course you can leave a job. It doesn't look great but if a much better job comes along you would be mad not to. If you had interview for 2 a week or two apart, and got offered the first one, you could accept and delay your start date to see how the second interview went. Like once you are offered one provisosionally it would often take a little while for them to send you the contract, first they would check references, if garda vetting is needed that adds a few weeks, occupational health assessment is needed for some roles. It is often several weeks from provisional offer to contract stage and it is only once contract is signed that someone would give their notice. So there is an expectation of some delay.

There is also the concern that future potential employers might look at your CV and think "Why is this person applying for a senior role in my firm when they can't even rise above the bottom of the ladder where they are?". It might not be applicable for your case but it is possible in general

It wouldn't apply if you qualified to do X (@50k) and while you were waiting for a role to open, you went and worked in Dunnes for a few months. But if the roles were broadly kinda similar, then it would be applicable.