No. The online app is tightly integrated with account logins for saving settings and custom scripts. As such, it currently requires an internet connection and cannot be downloaded for offline use.

No. I used to have an Android app, but due to low usage, limited time, and the fact that I don't own an Android device myself, I decided to pull the app from the Android store a few years ago. My online ear trainer is my best ear training tool, so I suggest giving it a try if you haven't already.

Just as you're unlikely to learn a foreign language in a few days, you're also unlikely to learn how to play a good jazz solo overnight. I think the best plan is to focus on rhythm and phrasing while playing as few notes as possible. When you have more time, you could read my entire learning to improvise series.