How much land do I need to own to make it a country?

There is no minimum.  To be recognized as a country you need two things.  You need to find land not claimed by another sovereign country (and will likely have to build an army to defend taking it from the sovereign country that claimed it before) and then find at least one other sovereign country to recognize you as a country.

The amount is irrelevant - any land you own will still be within a pre-existing country's borders. 

Its not about how much land you own, its about how big your army is.

Google 'micro nations'.

Ted Turner owned over 1M. acres and he wasn't even considered a state. Location, location, location. A country is more than land.

Technically, none.  Sovereign knights of Malta doesn't have any land.  To make a country with land, there's no minimum, but the land can't be part of any country that already exists or part of Antarctica.

There is no minimum size.  

More than what is available on this planet.

Any amount, you just have to get two existing countries to recognise it. It doesn't go by size at all.

Just steal others land and call it CHAZ.