The acoustic piano is preferred, but if you decide to buy a digital piano, it needs to have  88 weighted keys and if possible, hammer action. A low quality keyboard will not allow for a good piano technique. 

Pianists and long nails do not go  together! Imagine a basketball player with high heels. They may break, get stuck in the keys and your technique will suffer. And they create a click click percussion that we do not need.  

Thirty minutes are reserved for the  beginners first year. As the student progresses to more advanced repertoire, forty-five or sixty minutes is best.

Practice is very important when you are learning an instrument. I encourage my students to create the habit of practicing every day, even if just for a few minutes. Student may be dismissed if showing consistent lack of practice .