Can paralyzed diaphragm be the cause of cardiomyopathy? Seeing that's its all pushed up limiting normal function?

Unlikely. The heart muscle is quite strong in general. One diaphragm per side of chest, each with it's own nerve supply. The central portion under the heart is not the major moving part. Depending on the cause of phrenic nerve dysfunction it can get better and even completely recover. Cardiomyopathy may come from viral, ischemic, alcoholic and other illnesses.
No. A cardiomyopathy is a problem with the heart muscle. But you are right it can restrict both heart and lung expansion if its severe enough.