Hi Amiga2000,
You'll have to look for a monitor which you can connect to the VGA-port, because there are also lcd-monitors which you only can connect to a DVI-port.
About the monitor with a usb-hub, this hub isn't used for video-signals. This hub is just like any other usb-hub.
you can use a 24 inch screen, but you'll be wanting a very high resolution. I don't know if your picasso can handle that.
I don't see any difference in a monitor with tv-tuner or a tv with a vga-connector
