If it crashes it's a bug, and I think that one is known. I haven't worked on it in a while but the plan was to rework the entire plugin so that's easier to fix. The crash is do to some logic error on my part, but it usually occurs when setting the mass under one of the plugin's trigger or loop events. The reason is under those events the chipmunk library itself won't let you change the mass, collision shape,... etc of an object. To alleviate that the change is just delayed till it's allowed to. In short it introduced too many special cases which made it increasingly hard to debug and fix, so an internal rewrite is needed in order to simplify things. I unfortunately don't have the time or interest to work on plugins to that extent, but at least for the most part this plugin is in a working state.
Yeah, I never investigated handing layers with different parallax, rotations and such. I just left it as unimplemented. Tilemaps can't rotate as I recall, otherwise I would have let them if I could. That bug seems odd, looks like the tilemap's bounding box is being used.
Usually you'd keep the elasticity in the range of 0 to 1. I'd make the ground and the first ball 1, and the second ball 0.2 or something. When two objects collide their elasticities are multiplied together.