Where a switched duplex outlet is used in lieu of a light outlet and fixture, the receptacle shall be considered one of the wall mounted receptacles required here. At least one duplex receptacle shall be provided for a central vacuum system if the ducting is installed. Some US references talk about a limit of 12. 20A circuits may have different rules. It is open to considerable debate whether you should mix general lighting and outlets on individual circuits.
Knight recommends it.
Some netters don't. I tend towards the former for load balancing reasons. There's a new rule on outdoor outlets. Romex is a brand name for a type of plastic insulated wire. Sometimes called non-metallic sheath.