Northern Irish moving from Japan to Ireland

Hello.
I am originally from Northern Ireland and I have been living in Japan for almost three years with my Japanese spouse. I have dual British and Irish nationality, however my husband and I want to move to Ireland. I have booked a flight to Dublin for myself only as I wanted to get a job and a PPSN sorted before my husband arrives, I will have to do this from N.I as I will be staying with my family after I arrive.
I have a few questions, sorry if they have been asked before.

On my marriage certificate it says that I am British due to the fact when I got my visa with Japan i used my British passport, would this be a problem for airport immigration since my husband will be going through Dublin airport alone and he will be saying that he wants to apply for a spouse of an Irish citizen, will it be fine if he just explains to them that I have dual nationality?
Or do I need to go back to Japan and come through immigration with him together?

Also will I be able to rent an apartment in Ireland for my husband and I before he arrives if I explain to the estate agent the circumstances or does he need to be in the country first?

Any advice is appreciated.
Thankyou

The immigration will be fine. A marriage certificate (with English translations) and a copy of your both passports or entitlement to Irish citizenship (e.g. your birth certificate) will suffice.

Many people rent a property before they arrive. That’s not an issue. Just read an article a few days ago saying quite a number of people pay their deposit before seeing the property.

Just be careful of various scam. Some may ask you to do bank transfers before telling you any detail about the property. These are normally scammers from other parts of Europe. Use a property agency if necessary. Google a bit which areas are safer.

Thankyou for the reply and for the advice one more thing I’d like to ask, since we will be arriving separately do I need to write an invitation letter for him to show at the airport? If I do what would I need to include as I’ve never written an invitation before?

An invitation letter is only required if he needs a visa. Since he doesn't need a visa to enter Ireland, there's no need for this letter. A stack of documentations will be more useful (although not mandatory) e.g. copy of rental agreement/saving statement/bank statement/utility bills/work contract etc... anything you have in order to prove that you want to live and work in Ireland without relying on social benefits.

Thankyou for letting me know