If you are very few, this will scare some potential students away. A larger group attracts more people in and by itself. I run an extremely small university club, and I'm amazed at how often people who call me to ask questions want to know how many we are! I've learned not to try to conceal the fact that we are few, but to be proud of our little group.
If it turnes out that your marketing strategies do not give the results you expect so you will be running very small classes for a while, it is crucial not to appear disappointed over this. Once I showed my disappointed when half of the group disappeared at the same time. This was immediately mirrored in the students and the energy in the remaining group.
In my experience, those who do join a very small group and stay, those who think "wow, private lessons" rather than "not so many people here, can't be any good" are quality students, regardless how talented or untalented they are.
Be patient, it takes time.
What you definately want to avoid is going to class and there´s no students there. Students get ill, their children get ill, they have to work late and repair the car and attend their friends' birthday parties... so this can happen, even when you have a small but stable group. Maybe you'll consider giving only two or even one class a week, rather than spreading your students over three classes. Some students will come all the classes you have, but most won't. I would remain at few classes until the situation is really stable with the number of classes I have.
You can definately have good quality training with one or two students. Overteaching is an obvious danger, though. One needs the teacher's full attention some times, but also to rest from it and try on ones own.
I wish you luck