As farmer, is it good idea to develop station hero skills or legion heros, in CoP Hero development..

Development heroes can be useful for everyone not just farmers and probably of more use to other classes as the farmer already has production buffs. Unless you avoid all conflict (alliance rivalries, Kill events, Reign of chaos) then it will still be important to upgrade your combat heroes for strength and certain of their skills will let you have more troops which will be very useful for gathering.

In general for dev heroes check their skills for useful ones and try to upgrade them when you can. For combat heroes don't worry too much about upgrading blue or purple, but try to max the orange heroes that you get.