Once these medals/orders are granted is it a requirement to wear them at official functions or is it a personal choice?
It isn't a personal choice, it goes with the etiquette and sometimes the king decides how the Orders are worn. For example, at the wedding of Victoria and Daniel the king wore Orders with chains, at the weddings of Madeleine and Carl Philip not. The Order of the Seraphim is the most outstanding distinction in Sweden. All the members of the royal family wear the Order of the Seraphim, if the King wears it.
The members of the royal family wear the Order of the Seraphim plus the royal women wear the King's miniature portrait at the Nobel festivities, at the state visit banquets, at the official dinners hosted by the king, at the formal gatherings of the Royal Academies, at royal weddings etc. Some of these events are events where the tiaras are not worn, but the Order of the Seraphim is.
At the Nobel festivities king Carl Gustaf, Carl Philip and Daniel had also the Order of the Polar Star cross, on a black band around their neck. And various decorations in miniature.
Victoria's and Daniel's wedding has been the most festive event during the last years, then the king had:
The King is wearing the Order of the Seraphim and Order of Vasa on chains.
Around his neck The King wears the Order of the Sword, the Swedish military order.
The King is wearing two grand stars; the Swedish Order of the Seraphim's grand star at the top and the grand star of the Order of Vasa underneath.
On the chest (from inside outwards) The King will be wearing decorations in miniature: The Order of the Seraphim, Gustav V's Jubilee Order, Gustav VI Adolf's Commemorative Medal, the Order of the Sword, the Order of the Polar Star and the Order of Vasa.
The Royal Family's Attire - Sveriges Kungahus
Video of the guests arriving to the King's dinner
Se filmen från kungens middag för Nobelpristagarna _ Svensk Damtidning