Working as a freelancer in Scotland

I can't answer the first part of your question as I am English so there was no problem with me becoming self employed in Scotland. I set up as a Sole Trader in 1998, doing domestic appliance repairs, washing machines, cookers etc. It was extremely easy, I did not have to register anywhere or go through any legal procedures, I simply started trading. Obviously I needed to keep accurate records for tax returns but even those are simplified when your turnover is below a certain figure. I never needed an accountant. I was not even experienced in the work I was doing, although I am a qualified engineer. It was therefore quite a steep learning curve to acquire the tricks of the trade. It would be easier now as there are trade forum websites where people share their experiences.
One worry was that there might be descrimination because I was an "incomer" from England but I hardly ever had such problems and most of the customers were very friendly.
I was in the north east of Scotland, between Aberdeen and Inverness and it did take me a while to pick up the local dialect. Anyone who has visited Aberdeen will know what I mean. It is a fairly thinly populated region so there was never a huge amount of work but I was willing to make financial sacrifices to live in such a beautiful part of the world.