I will chip in on the bits that I can answer and hope someone else can help you out on the other bits.
In Handcent if you long press on the text you want to copy you get a pop up message offering copy. You can then paste it into a new message. You can use the touch screen to select anything you want to erase and use the back button to remove text.
There is no zoom on the mini's or X8 and I don't believe there is any app that can give you that functionality.
On the music player front I have heard good things about Zimly or MixZing apps but not a music player person so hopefully someone else can comment.