It will be very difficult to find a job as a pilot in Europe without the unlimited and unrestricted right to live and work throughout the EU/EEA/CH. Permanent residence in an EU country only gives you the unlimited right to live and work in that one country.
That depends. If one wants to find employment in another EU county that could prove difficult. However, with the right to work and reside in germany you can certainly be employed by all german airlines without a problem. You might face certain restrictions on duties, but that is all manageable. In my (german) airline we do employ several foreign citizens including US and Canadian citizens. In fact, the board member for international relations in the german pilot union (Vereinigung Cockpit) is a US citizen.
The issue about the transference of the german medical into another country is very much true, especially the UK does not allow it without the medical records which can not be transfered according to german privacy laws. However, another initial medical in another country can solve that problem, but of course has the stronger limits associated that the initial medical has.
And yes, in germany you need a radio certificate as well as language proficiency (german and english). In germany it is called AZF. It can be limited to english only, but in that case you are not allowed to fly VFR in germany as the german language is the primary one for VFR operations.