What is your goal in making him take piano lessons? Can it be accomplished on another instrument besides piano?

I enrolled both of my older children in piano lessons when they each turned 5. My daughter loved it and practiced on her own. It was a constant battle with my son. I finally decided to make him an offer - pick any instrument that required musicality and reading music (no just drums, although he could also play drums in addition to another instrument). He was thrilled and chose clarinet. He played in the school band through his Freshman year when the conductor forced him to choose between missing band practice and missing climbing practice. He quit band, but he still plays his clarinet on his own.

Perhaps your son hates the piano. I know I hated piano. I begged my mom to let me take violin lessons, but she made me take piano through my senior year in high school. I don't play at all now, because it is associated with so many angry, unhappy feelings.

As to your #4 and #6 - my sister and I had 45 minute lessons. She practiced 2 hours a day without being pressured to do so. I sat and complained at the piano until the egg timer went off for my required time of practicing. My mother was intricately involved with my practicing - telling me which pieces to do when, disagreeing with the approach of the teacher, and inputting her opinion in the way I played my songs. It made me hate piano not just for the piano but because it was not "mine" but was about my mom pushing herself on me in something I hated to begin with. From my own experience, I'd suggest finding ways to pull back and leave this between your son and his teacher so that it's about the music, not about the dynamic between you and him.

My advice is to "pick the hill you want to die on", because this has become a struggle of wills where someone is going to lose. Is it really worth winning to force an 8-year-old to play an instrument he doesn't like? If there is another way to reach your overall goal without making this a power struggle, I'd highly encourage you to get creative to solve it to get what you need out of it and still let your son feel like he has some say over his life.