Servants could fulfill different tasks in a household of a noble family. In the royal household of 1775 there are for instance several servants that would open the doors or even some that would just bring the wine for the king. Even they were paid a proper income per year and earned a living that way.
In order to keep the currency system as realistic as possible nobles will not only have to pay for employees but also for the property they claim (for ex.: their châteaux or even their carriages which require a certain amount of staff). A list of these requirements can be found here.
This is supposed to keep the expenses on a realistic level. They are not necessarily real or "exist". In other words: If you claim a château you should be able to afford it. In addition to that even a fictional chateaux will require a staff for maintenance. In fact chateaux were not only status symbols like cars today but they were an intensive investment that brought about the financial ruin of many families.
Income of EmployeesEdit
Servants would also receive fixed income per year. Thus, they bore a financial risk for families as a result. In the following you can see a list of different valets serving the king in 1775:
Huissiers: 300 l per year
Sommeliers: 300 - 600 l
Sommiers: 600 l
Coureurs de vin: 600 l
Hâteur: 400 l
Portagers: 400 l
Patissiers: 300 l
Avertisseurs: 300 l
Serre d'Eaux: 225 l for half a year
Galopins Ordinaires: 300 l
Écuyer: 1200 l for half a year and 600 l for a quarter
several "Aydes" serving and assisting the valets mentionned above
This just gives you an idea of the size of some households at court. The various service offices and their income would vary considerably according to rank. Just like the nobility the employees at court were subject to a strong hierarchy.
An ordinary servant would earn between 300 - 600 livres per year in a royal household (6000-12000 sou) which is indeed a remarkable income for a member of the lower class.
The income of a servant in a private household can be fixed by the family itself. However it should be AT LEAST 400 livres per year.