There's no real reason to attack a level 9. You can't farm anything above a level 5 without losses, and a level 10 is what you really want. As far as conquering a level 10, there are numerous guides out there, all you have to do is a little looking.

Oh and once you have the appropriate troops to conquer a level 10, then you can farm them too. Not without losses, but many players find that it's necessary to keep up with their food production, or lack thereof.