It would, of course, depend on the size and design of the house you are having built. If it is two storey, then it would be best to have ducting fitted. The main units then go on the roof and, hopefully, out of sight with tubing connecting smaller interior units which can be hidden under false ceilings, normally in the kitchen an bathroom. The ducting then diverts the air (cold or hot) to grilles in each room which is virtually silent. One unit per storey
You need the inverter type aircon units. These get to the required temp and then maintain a steady airflow rather than switching them off and on which will cost more to get back to the required temperature. The heating part just heats up the outside the air and doesn't use a heating element so they are very cheap to use. Probably average out about 8 or 9 cents an hour for heating (and that can be for up to 3 rooms) or 12 cents for cooling (again, for up to 3 rooms). The initial outlay will be more expensive but well worth it in the long run especially as you are having it built from scratch. We already had the ducting pre-installed by the builders and the aircon units (Fujitsu) cost €3500 including fitting. The units, when in use, make less noise than the fridge and are very economical to run.
As you're building from scratch, make sure you get good insulation especially around windows which is something rather lacking in Spain.