How can I find out the best place to establish an interior
design/decoration and art advisory consultancy/ art dealer/ gallery
business in the UK and/or Europe?

Hi Clarette,
It is not clear whether you want to establish a business providing all
that or if they are alternatives:  advisory consultancy or art
dealer/gallery.
The best location would depend on what experience and capital you have.
There are also formalities with setting up a business in a foreign
country and getting a visa that would allow one to work there.
Good luck, Myoarin