I used to travel regularly and stay in Stockholm mostly but that was some years ago. I enjoyed it very much, there was a lot of things to do and you could be out and about a lot, but it was always an expensive place to live in, to my recollection.
On the plus side all the places I stayed at whether in chalet style bungalow or block of flats in Stockholm were very well insulated and the triple glazed windows also kept noise down.
I think it will be an exciting time of change for him, but on the cautious side, I would recommend that he saves up enough money to get back to UK if necessary, that he reads up on such things as working permits, whether his qualifications are accepted in his field in Sweden and checks up on things like pension stamps etc. I think when I lived abroad we paid something like class 3 for the national health, which of course we did not use whilst we were abroad but it sort of kept up our entitlement for when we returned to the uk. You might also like to read up more about life in sweden and think of what you might like to do if you visit there.
Whether it turns out to be short or long term, in my view to live in another country for a time gives you a broader view of life, a more clear understanding of not only how life works in another country but makes you aware of how you live in this country and you are then making choices in your life , rather than just going along with the flow. I dont know if it is that people who travel and live abroad become more aware , or travel because they are aware of the very different ways of life that one might choose , but I have always found those who chose to do this , have a broader outlook on life and are less pedantic and determined to see their home way of life as the only correct one. Hope he enjoys his time there and that you also enjoy finding out more about Sweden, its food, customs, and people. Good luck to you both.