The cover is a very thin, transparent plastic cover, similar to the thin cover that you get on the screens of new mobile phones. You can use those covers to cover the top, bottom and screen of your MacBook. For the keyboard, you need to buy a washable keyboard cover that will cost you another Rs. 300.
The specs of the MacBooks:
http://www.apple.com/macbook/specs.html
The lowest end model only comes with a combo drive.
There isn't much price difference between the lowest model and the second one. So, it would be wiser to opt for that one.
As for the availability of the installments option, you'll have to ask the vendor.