I think the first thing you need to do is figure out your “burn rate” - what are you currently spending every year as a couple?
Great point. I didn't know offhand but I've looked back over my spreadsheets. Non-discretionary spend ~27-30k, Discretionary ~15k. I don't really know what's average, but we're a bit anti-consumerist, so not big spenders. It's just not of interest to us.
What are the statuses of both your COAP’s? You probably have about 30 of the required 40 years of contributions?
Correct, I have just 30years. This concerns me ... it would be a key reason to take parttime employment, ie. not for the income now, but to make up 40 years contributions by the time I reach retirement, age 67? As I don't have a DB pension, I consider a full state pension very valuable. I actully have very little idea of how to make my shares/assets/pension work for me. I just always availed of any company saving scheme (shares/AVCs) to the max.
If you plan to be occupied running the house it’s a job with zero job security. Just something to bear in mind. Your kids could move out with their partners etc.

No, I do not need them to keep me busy - they've largely been responsible for their own laundry, transportation and capable of cooking for themselves since they've been about 12. However I see that them owning their own place as opposed to renting is very difficult. A large part of our financial independence has come from buying our house early in life. I view travel as incredibly formative and would encourage them to spend a year+ abroad, but while we are all getting along well (more as equals than a nuclear family), while they choose to live in Dublin it makes a lot of sense for them to live at home. They're good craic too.
To be even more honest, I'm shy to admit it, but I guess I do aspire to an alternative life. I would like the chance to begin again. It seems in a way like the easiest thing (if I could) to go back to a job similar to before. That would be the safe option.
I feel like I've had a good innings, but I'm looking for a second round.
I think I'm really looking for assurances that I'm not being reckless here, that we're meeting our responsibilities to our family, but life is short and (provided my spouse is onboard

) I'd like the adventure to begin from scratch (maybe as a carpenter's apprentice, or an artist, or an activist, or student, or ...)