As above, your biggest challenge might be buying insurance for the UK registered bike if:
A. You do not hold a UK driving licence, or
B. More likely, that you do not have a permanent UK address
C. If it is not a UK registered bike
When it comes to insurance, the vast majority of UK motor insurers operate on a ‘Pile it high, sell it cheap’ basis, catering for the many thousands of run-of-the-mill customers who fit into simple boxes. The simplest two boxes being: Do they hold a UK licence, do they have a permanent UK address and is it a UK registered bike? The vast majority of the members of UKGSer - and the UK motoring population at large - will fit into those boxes very neatly.
My suggestion would be for you to ask the same question on the HUBB (Horizons Unlimited) forum where you’ll probably find more non-UK citizens making the same enquiry and / or be able to give you an accurate up-to-date answer.
https://www.horizonsunlimited.com/hubb/
Another alternative might be to hire a motorcycle here in the UK, the hire company being more easily able to arrange insurance on their customers’ behalf.
One last alternative might be for you to approach one of the very few UK insurers who does not necessarily rely on customers that do not fit into a neat little call centre or online box. One of these might be able to help you. One to start with might be:
https://www.rhspecialistinsurance.co.uk/
But that is just a wild guess.
When it comes to medical insurance, my advice would be not to approach a UK insurer but to speak to your home based insurer, who should be able to provide you with a suitable worldwide policy. This will get you around the likely problem that you do not fit into a tidy little box, demanded by a UK insurer. We in the UK find it really easy to buy worldwide medical insurance from a UK based insurer, as we fit into a tidy little box. My guess is that you will have as many or more insurers offering the same worldwide service for your country’s citizens travelling abroad.
As to the rest? Once you get over the hurdle of buying, registering and insuring the motorcycle, all the rest is easy once you cross the narrow strip of water (do not call it ‘ocean’) that divides the UK from the mainland of Europe and our friends in Ireland. Similarly, riding around in the UK itself is easy, too. Though we (and the Irish) do, uniquely, drive on the left. That is not as huge a problem as it might sound, so don’t worry about it.
As to whether to ride through France or catch a ferry to Spain? Everyman and his dog will have a different opinion on that, sometimes predicated on no more than where they happen to live in the UK, small country that we are. Similarly, there will be all sorts of advice as to whether to use motorways or not, even on whether to avoid cities and some larger towns. The simplest answer is: Do what YOU want to do, within the constraints and / or flexibility of the time available and demands of YOUR holiday, not theirs.
PS Take comfort that you’ll not be the first non-UK national to make the same journey and hopefully you won’t be the last. All your predecessors managed it, so you’ll be able to, too.
PPS You might find this thread useful:
https://www.ukgser.com/forums/showt...ike-insurance-for-non-UK-licence-holder/page2 As is common, you are not the same as the fellows in the example but it might give you an idea of who to possibly talk to for motor insurance.