A farm can represent almost any type of farm or agricultural holding. It could be vinyards, orchards of fruit or more prosaically sheep, cattle or crops. It shouldn't be a forest or wood - if that is what you want to take then we would recommend you choose the forest resource instead.
The size of a farm can vary dramatically, depending on how productive the land is and what crops are grown, a normal size for a farm would be around twenty acres but an orchard might be much smaller, only a few acres, while a sheep farm on the Urizen hills could easily be ten times this size.
A farm produces 9 crowns.
There are no downtime options for a farm. It produces income automatically.
A farm can be upgraded using weirwood obtained from the Bourse. Each time a farm is upgraded, the owner receives an additional income of 36 rings from then on.
To upgrade a farm requires Imperial wains of weirwood equal to the level the farm is being upgraded to. So the first upgrade of a starting level 1 farm costs 2 Imperial wains of weirwood, from 2 to 3 costs 3 Imperial wains, etc.
A farm can be diversified to sacrifice income for resources or herbs. To diversify a farm costs one throne. Each time a farm diversifies, the owner chooses one resource produced by a forest or a single herb; the farm produces 2 measures of the chosen natural material or two doses of the herb but produces 36 rings less income.
Senators in The Marches are chosen by the steward who controls the most land in furlongs (an old Imperial unit of agricultural measure). This is represented by the farm personal resource. A Marcher character who has been operating a farm personal resource in a Marcher territory contributes 20 furlongs to the steward whose group they are in or to whom their group has sworn fealty. If a farm is upgraded - then the character who operates that farm contributes 4 additional furlongs for each upgrade.