What a great assignment!
This is a great opportunity to spend time with the folks who work at the Building and Health Departments. What is the time line on the sewer? Has it been designed yet? Funded, even partially? Are alternatives to a tank & leach field, such as a mound system, allowed? Get as much info as you can along with the name a number of the persons you speak with.
The value of the property may be $50k as horse pasture plus a speculative kicker. Buy and hold? Maybe a mound system will be allowed on a permanent or temporary basis so maybe you have a building site with higher than normal development costs?
Just as an aside, there is a community here which is about 50% developed but stopped issuing water permits in the 1970s due to the limits of the community well. Homes are 500k & up and the $600-700k home would be 1,500sf and of average quality and condition (virtually all built pre-1970). There are plenty of subdivided lots in the area which typically sell between $2-4 per sf depending who the buyer is (buyers who are adjacent landowners pay the most). Lots are typically 4,000-10,000 sf and a dozen or two change hands every year. Somehow the water district "found" more water and decided to issue one more water permit a few years back. Is was sold through a sealed auction for ....... $325,000.
Moral, there is a big difference between 5 acres of land and a 5 acre building site. Do you best, document what you did, listen to anyone who will talk to you, and most of all ... enjoy!