I am not sure you will be able to receive cablevision channels with your receiver---in addition,, I do not know how long cablevision will continue to broadcast the channels unscrambled, so your best choice is probably is probably arabsat. I don't know what you watch on Nilesat, but chances are that it will be on Arabsat, so you can probably point your Nilesat dish at Hotbird and don't have to bother installing another dish. I think anything 50cm or more should work.
Also, be aware that you may still have to get an HD compatible receiver---I think LBC and MTV's broadcasts are in HD, but you can cross that bridge when you get to it.
Also, be aware that you may still have to get an HD compatible receiver---I think LBC and MTV's broadcasts are in HD, but you can cross that bridge when you get to it.