With regards to your question on hinging the farm gates, you will need to set the posts in concrete and ensure that the posts have been treated against insect infestations.
You will also need to set the posts deep enough to carry the weight of the gate. Follow the simple third rule; whatever is the longer - posts or span of gate, bury the posts to one third of that length.
With regards to the hinges, make sure that they are heavy duty hinges to carry the weight, preferably in a material that will not rust; brass, wrought iron, etc. These should be face-mounted, strap hinges.
The hinges can be found in various architectural styles to match the gate fastenings, to maintain that traditional look.
If you have any further questions, don't hesitate to write in again.