Is there difference between 'casa minha' and 'minha casa'?
There is no difference. You can use the possessives in on word "meu, minha, seu, sua, teu, tua, nosso, nossa" before and after the noun. But I want to make you sure if you put right after the thing people will think you want to be elegant.
By any chance, could green in this sentence also mean energy efficient? I'm merely curious.
Yes, you are right! But I think it needs to be used in a correct context in order people grasp its meaning.