1.Does Vhare come with installation instructions ? The whole set of instructions like FFmpeg and everything else needed in order to run the script correctly.

You can see the vshare install instaructions at http://www.buyscripts.in/vshare2-installation.html.
Aslo http://docs.buyscripts.in/Server_Setup

2.What is the standard theme of Vhare and can the banners and website layout be modified easily?

you can see the demo site at http://video.bizhat.com. You need to change the layout manually. edit and modify the files in the templates folder.

3.Can ads be placed on every page or just on the main page ?

The top and bottom banner shows every page