An airlock is a good idea, some people do foil for short periods, but you risk the beer turning to vinegar. Sours can age anywhere from 60-80 F, lower temps take longer but tend to give a more balanced result.
Pitching now when the gravity is low and the alcohol is high will probably make for a mildly sour beer. You may or may not see a pellicle, don't worry either way.
Just like any other beer bottle when the gravity is stable, although in this case it should be stable for say a month. I would wait at least six months before checking, it will take a bit for the bugs to really get to work.
Hope that helps, good luck.