I think all of the cities which traditionally used the Western Approaches to trade with the rest of the world will benefit, including Northern Ireland.
Ireland itself though I think will take quite a large hit. There are many businesses which set up shop there to avoid UK taxes, Think Lidl, Aldi, Amazon and Ebay... I'm sure there are lots more but these are all very large. Amazon alone probably has a turnover close to $10 billion a year yet hardly pays any tax to the UK treasury ( think it was about £10 million a few years ago when it should have been billions).
They'll be forced to pay taxes in the UK instead which will mean that Ireland loses it's advantage here. I don't know the figures, but I rather suspect this will be billions, maybe even £10 billion or more per year. Quite damaging to Ireland's small economy I think.
Of course though this is merely correcting a wrong, the fact that so many businesses with huge turnovers pay hardly any UK tax is a scandal and has often been highlighted by campaigners.
As for the border I doubt it will be an issue at first, of course if smuggling became a real problem then things might have to change. I can't see how immigration would be effected, someone crossing the border into NI would still have to show where they were from, and likewise the opposite, in order to claim benefits or whatever.