There are two ways. 1. The directional button (it has the "OK" button in its center) can help you index to the photo-only view. Just press "down" a few times and you'll wind up at an image-only view. That view will stay in place as you index through images (by pressing the navigation button to the right to go "forward" through images, or to the left to go "backward" through the images until you press up or down again, getting you back into the image and info area. 2. In the menus there is a place where you can turn all that stuff off (or get even more info to display). I don't understand your second question....

the audio bit should be about 16bit and 44.1khz or 48khz that's the standard

You need to use a type C mini hdmi cable which can be purchased from just about anywhere.

The SB-28 will work but there are some limitations, it can only be used in non-TTL auto and manual modes, if you try and use it in TTL the shutter button will lock.

Check page 103 of your Users Manual. In the "Shooting Options" menu there is a selection for ISO Sensitivity. If you turn that off, ISO becomes a manually-controllable setting. Page 103 shows you how to do it and which buttons to push to set ISO at your desired setting. You can then use "A", "P" or "M" mode to control aperture. In regard to flash, I have found that using a snap on flash diffuser makes the photos more natural. If the classroom is lit with flourescent light, you can accomodate by using the very effective White Balance function in the D7000 (or a gel on the flash).