Just completed my EASA conversion. For the theory exams I used the Bristol Ground School distance learning program and supplemented it with a question bank. Overall it took me about a ten months from getting serious about it to actually having the license in hand.

If you are serious about working in Europe, I would strongly consider doing what it takes to change the permanent residence into German (and thus EU) citizenship. 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. Although I do believe Germany generally does not allow naturalized citizens to maintain dual citizenship with another country, which would mean relinquishing your U.S. citizenship.