As a Brit based in Germany, I am concerned and bewildered by the uncertainty which Brexit may bring.
I think most Brits have already done considerable homework on the matter, even if the fact that the continuing failure of the negotiations means nothing is yet cast in stone. I am one of the Brits who has left everything to the last-minute, partly because I am overseas for a lot of the time so have enough other uncertainties of my own.
I was doing a bit of Googling recently and I did stumble across a UK Government website which has some useful information and advice, even if it is still pretty scant. The website is https://www.gov.uk/guidance/living-in-germany#visas-and-residency
I know the German government has also issued some information and when I find it, I will publish it on here.