You will need to check the building regulations Mwncigirl. The maximum plot size for a new build is 2500m2, so just over half an acre. They are trying to reduce that even further to 1500m2 because 3% of agricultural land in France has been lost in the previous 10 years due to people buying large areas just for residential. There may be an agricultural business over-ride though? I was told there was, but that is 4 years ago and lots of things have changed.
You may be best buying a derelict and knocking it down. But there is another factor in play now and that is the local farming society called SAFER. They have legal first option on any agreed purchase, their objective is to buy the property and strip the land away from the house, then sell the house on its own. This happens an awful lot here, so it is near impossible to buy a cheap house with good land over 2Ha. But the degree to which SAFER pursue land varies from area to area so you would need to ask and make sure the wording of the Compromis de Vent doesn't leave you liable for the Immobillier fees anyway.
Looks like you are close enough to the mountains to get snow! We've had one fall in 3 years here and everything ground to a halt because there is no road gritting. The only time we see it is when the clouds lift to reveal the Pyrenees, 80Km to the South of us. Do still miss it though- we have snow chains we bought in the Dordogne, but have not yet used them here.