I have been working in Italy for the past 4 years on yachts. The last 2 years been using the Italian D type visa.

I am now wanting to set up shop and move here permanently. Does anyone have any recommendations or ideas of the best way to move here post Brexit.

It depends on the type of D type visa you had.. work, study, elective residency etc, and then who paid you and how you were paid. It also depends on what you plan to do once you are here 'permanently' as to which type of visa to apply for.