" a working welfare state, a welcoming society, and an influx of enthusiastic citizens from all across the EU."
? The welfare state is not really changing, why would this be part of your point?
? The UK is always among the most welcoming nation in Europe to new migrants. The ideology betraying 'Brexit' as somehow implying the UK is toxic to others is false, people keeping saying this but the data says the exact opposite.
Various Pew Surveys concerning attitudes towards migrants put the UK always within the top couple of nations with respect to tolerance on various issues. [1] Literally, the UK is one of the countries least likely to want 'fewer migrants' (this is 2018) [2].
Here's some more data [3]
Also, for example, the mayor of London is Muslim, and up until last week, the #2 most powerful person in the UK was Muslim, the #3 most powerful person is a woman of Indian heritage. There's been very little fuss over that.
So I think it's basically inconsistent with reality to lament the UK as somehow 'unwelcome' especially relative to most EU nations (almost all of E. and S. Europe) which are borderline hostile.
? EU citizens will be able to come to the UK, but now that it's not a part of the EU, obviously, there'll be some kind of paperwork required. If you have an education, a specific job, or you marry your partner etc. I suggest it won't be that hard.
Finally, I would say that odds are even the UK gives more points to EU citizens after trade negotiations than they do people of other nations. Within about 2 years it will be easier for EU citizens than others.
[1] https://www.pewresearch.org/global/2014/05/12/chapter-3-most...
[2] https://www.pewresearch.org/global/2019/03/19/europeans-cred...
[3] https://migrationobservatory.ox.ac.uk/resources/briefings/uk...