If you can, buy land in a valley.. better soil, flat…. and some steeper land on the side of the valley. Steeper land is often MUCH cheaper. This might give you the possibility of a stream which flows out of the hills providing you with gravity fed water supply, and also the possibility of micro hydro power production.
I have this situation largely by luck.. we did not consider it at the time. You may be able to source water from nearby hills which are owned by forestry interests .. or are not farmed. A forestry guy once told me that they often find “water system” pipes coming from their land. Most of the time it is not a problem.. except when they harvest.
The bottom of valleys are often frost prone.. and the sides of the valley or on slopes..there may be sites with frost drainage which allow frost tender crops to grow.. giving you more variety. Steep forested slopes which cannot be farmed or driven on.. give you a place to retreat and hide in times of danger. They may also hold wildlife which you can harvest in time of need.