First, check you have water rights - many properties have had the warter rights "stripped" and sold by a prior owner, and in some states the water rights stayed with the county originally. Check with your local water board or planning board, and read your title. The rights are probably also limited by state law and local waer conservation districts to certain extraction amounts, and may require a permit and a meter to report consumption.
On the iron issue (or manganese or potassium or magnesium or lime etc) - check again with your local water district about groundwater quaslity, or see if a neighbor has test results (this is best way). The driller you choose may also have typical test data before you decide to drill. Theres should be a state geologist report on the groundwater in your area, that should have smaple test data and information about which aquifers are "good" and which have proboems, if there are multiple aquifers. This may have a lot of effect on your well depth, because the first aquifer you hit may well not be the best water.
As for iron treatment - there are a LOT of issues here - you really need to get data from the local government agencies (they commonly have treatment recommendations too), THEN talk to a water purification contractor.
Here is a pretty good article on the hard water issue and the multiple of ways to treat is - oxidation, chlorination, sand precipitation, resin exchange, flocculation and filtration, etc -
You are really going to need specific water quality test data from your well before you can decide on the treatment needed and of course full water treatment is pretty expensive to use for irrigation water, so you may want to set up a primary treatment like sand bed and chlorination or oxidation for everything, then pull the irrigation water off before treating household water with more traditional water "softening" means, otherwise you are going to spend a lot of money on resin, sand changes, and filters.