"Id have assumed an all-or-nothing approach and knock at least the UK, French & Chinese nuclear counterstrike capacity, which I think personaly is achievable in this kind of scenario?"
I think: no. It was possible with China, but it was almost impossible to knock out all French and UK nuclear counterstrike capacity. Hitting France or UK with strategic nukes (SS-20 or worse) means only: lose Moscow. Just one French or British "boomer" submarine could bypass the Soviet ABM system and destroy the Soviet capital. Even if Soviets were sure to sink all the French and British boomers in the first minute of war, they were not sure to avoid a possible US massive retaliation in defense of France or UK. Including UK and France in your war plan, implied an inevitable global exchange and mutual suicide. If you (Andropov) are acting for your own survival and you want to preempt a NATO first strike, I don't think that suicide is the best strategy, even for a paranoid leader as was Andropov. So, I think that the "Seven Days to the Rhine" scenario makes some sense.
"Plus i cant see NATO not responding with a full SIOP in such a limited scenario"
I see it, indeed. Flexible response meant: use tactical nukes against tactical nukes and launch strategic weapons only in case of a Soviet massive launch against the central systems (UK, France and all CONUS: Usa, Greenland and Iceland). It's comprehensible. If you were Reagan, would you have risked the loss of Chicago (or Washington DC) just after the blast of few dozens tactical nukes in Central Europe?
The question would be "can you risk not doing something?" "And how much can you do and not escalate the exchange?" After a brief exchange like mentioned I would think the American people would have a very negative view of the USSR. I doubt they would blame NATO. IMHO, I was 27 at the time, the US would go balls to the wall on building more ICBM'S and an ABM system. It would probably end with the "Evil Empire" launching a first strike in a few years, they see they can't keep up and starving since no one will sell them the food the need and possibly the US launching a first strike, since they have nothing to lose.