Having caught up with a few pages so far (I'm presently at the end of page 287 from 297 in total at the time of this post), to me the Irish conundrum would be complex assuming the status quo is retained. As mentioned in previous posts, the UK and Ireland have the Common Travel Agreement which may or may not be compatible with the freedom of movement between the UK, Ireland, and the remaining EU post Brexit.
Furthermore, Northern Ireland mostly voted to remain, alongside with Scotland and Gibraltar. The suggestions of hard borders between the UK and Ireland I believe neither the UK nor any of the Northern Irish people would want to return to those days before the Good Friday Agreement (if my memory is right), which helped remove the borders/checkpoints between Northern Ireland and the Republic.
In relation to Scotland, Nicola Sturgeon has made several offers to Theresa May for Scotland to be involved in Brexit discussions, but has not come to fruition. There is a democratic deficit in that Scotland, Northern Ireland, and Gibraltar all voted to remain, but do not have much input in trying to get a good Brexit deal. Although I am not a supporter of the SNP's version of Scottish independence (I am more of a progressive federalism person that would like to see power devolved to the regions and not just to Edinburgh, Cardiff, and Stormont), in the twenty years or so that I have resided in Scotland, I do understand the various catalysts of civic Scottish nationalism. One of these is the results of the General Elections since 1979 in relation to how Scotland has voted, which I have summarised below.
1979: Mainly Labour, got Conservatives
1983: Mainly Labour, got Conservatives
1987: Mainly Labour, got Conservatives
1992: Mainly Labour, got Conservatives (only just, due to a late swing during the day)
1997: Mainly Labour, got New Labour (which were not new, and were most certainly not Labour)
2001: Mainly Labour, got New Labour (which were not new, and were most certainly not Labour)
2005: Mainly Labour, got New Labour (which were not new, and were most certainly not Labour)
2010: Mainly Labour, got Conservative-Lib Dem coalition. It is noted that with the exception of my constituency Glasgow North East that was held by the former Speaker Michael Martin (the 2005 election was obviously a neutral candidate) and reverted to Labour in 2010, all of the constituencies did not change parties at all. This sent a clear message to David Cameron and Gideon George Osborne that they had no mandate to impose cuts on Scotland.
2015: Overwhelmingly SNP, got Conservatives (only just, due to errors in polling methods of the surveys that initially had a possibility of a rainbow coalition)
2017: Mainly SNP (albeit heavily reduced compared to 56 MPs in 2015), got minority Conservative with some support from Northern Ireland's DUP (which the top people were once ringleaders in the UVF during the Troubles)
As can be seen from the above summary of General Elections since 1979, Scotland has not had the government it has voted for. Depending upon how the Brexit negotiations progress and what is offered to the UK, I do understand the recent suggestions of a second Scottish independence referendum, even though I would not be enthusiastic about it so soon after the 2014 referendum.