Re: Indoor practice
Something to else to practice is casting across chest and down to horizontal. Once you have that try and teach yourself to cast with your off hand. I have found having these skills to be invaluable on stream through the years, casting with your off hand is going to make you feel like you've never cast a fly rod before. It's the same principles as you've already learned, and you'd be surprised how doing this will take the edges off of your good casting arm because this will take you back to the beginning basics making you think about things in your stroke you haven't thought about for a long time.
There is a need to fish, to be in the water. It soothes the soul.