Or, of course, the characters can be servants themselves.
So she went along and went along and went along, till she came to the end of the wood, and saw a fine castle. So there she hid her fine dresses, and went up to the castle gates, and asked for work. The lady of the castle saw her, and told her, ‘I’m sorry I have no better place, but if you like you may be our scullion.’ So down she went into the kitchen, and they called her Catskin, because of her dress. But the cook was very cruel to her and led her a sad life.Except of course that you would want to omit as many of them as possible in the grand old tradition of not drowning your reader in casts of thousands. Catherine Moreland got a quite ludicrous idea about the number of servants at a great hall from fiction:
The number of servants continually appearing did not strike her less than the number of their offices. Wherever they went, some pattened girl stopped to curtsy, or some footman in dishabille sneaked off. Yet this was an abbey! How inexpressibly different in these domestic arrangements from such as she had read about — from abbeys and castles, in which, though certainly larger than Northanger, all the dirty work of the house was to be done by two pair of female hands at the utmost. How they could get through it all had often amazed Mrs. Allen; and, when Catherine saw what was necessary here, she began to be amazed herself.Then, most of these characters make their appearance only here. I'm not sure how many servants appear in Northanger Abbey outside of this tour, but I'm sure it's not more than a few -- possibly not even any.
Which of course makes them less than adequate sources for trying to figure out how many servants your character needs -- or rather, what is the least number of servants that would be plausible, and let you economize on the characters for the story.
Hmm. Unless the characters are servants, in which case you need enough to orchestrate them, but still, even there, there's an upper bound as well as a lower bound to how many servants you can have.
Most households, in most times, you can work out from secondary sources about households, but it's oddly difficult to find out whether they would bring the servants when traveling -- or rather, how many of them they would bring, if any.