ocean current predictions are one of the hardest to do. (there is way more uncertainty here than in global temps because to a first order, currents make 1 place hotter and another colder, averaging out to 0 on the global scale). the predictions you should trust most are global temperatures. you can get a pretty good estimate of those with pen and paper. sea level rise is also very solid. you can more or less replicate those with a laptop and a few hours of coding (the dominant mechinism is the ocean expanding because it's hotter). location specific effects have much more uncertainty. A good way to view them now is to not look at them as fixed, but a range of possible outcomes. the real harm from climate change isn't that any specific change will be catastrophic but that change in general on this scale is catastrophic. any reasonable set of changes of the scale climate change will cause will result in wars over water rights, increased intensity storms, hundreds of millions of people forced to leave their homes because they are underwater or unlivably hot or to dry to sustain their current population, mass extinctions (an estimated 7% of species that existed 10000 years ago are already extinct which is a rate somewhere between 100 and 10000 times the normal extinction rate).

No, the Gulf Stream keeping western Europe warmer than the rest is still the general understanding, by several degrees C.

The gulf stream may well stop (under some scenarios), but the effect of that on N. European climate will not be to make it like Siberia. It would more likely be like the Pacific Northwest. For example Seattle and Vancouver are at similar latitudes as Paris and London, and don't benefit from something like the Gulf stream.