Huh copy/paste works fine with vertical splits. Just setup tmux to sync your tmux clipboard with your regular x (or osx if you're into that kind of thing) clipboard.

You mean selecting text with a mouse on a vertical split? If so get tmux upgraded to 1.8+ then prefix-z and you can temporarily zoom the window to full screen.

Your information on tmux is highly out of date.

Also prefix-alt-2 will move to horizontal layout of panes.