I have a complex system with water treatment. At the well, there is a pump dropped into the well (20 feet) and one pressure tank. It is pumped across a field to my 5000 gallon storage tank. Out of the storage tank it first goes through two pressure tanks and then to either to a "treated" line or untreated line. I have untreated water all around the property so treated water is not used for watering, etc. The treated side goes through 3 systems - nitrate removal, calcite (raise pH), and a water softener. This goes to the house and to other hose bibs. The two pressure tanks ensure the pump is not turning off and on too much. The 100 gallons in the pressure tanks is used before the pump turns back on.
As far as testing, you must have this done before installing any kind of filtering or treatment system. This will cost hundreds but is necessary. You need to know what impurities are there, hardness, etc. There's a huge list. I have 18 years installing and maintaining this system. Also, not all pump companies are equal. Be very careful who you hire. Read a lot online.