Balance. An extreme of "something" is not good...
What do you mean by "balance"? Is it that which you and the culture that conditioned you would consider "normal"?
That's a good question. But such things go together with a certain lifestyle. For example, when you start having children, it becomes terribly hard to have such a lifestyle. Not only do they need toys and more clothes. But you will require a bigger house, a bigger house goes together with tools for fix stuff, etc.
The question is whether you should define minimalism quantitatively or qualitatively. Isn't minimalism to buy what you need to lead a reasonable life, rather than a race to have the lowers number of possessions? The minimum number depends on so many factors: family size, illnesses, hobbies (some people require only a GPS for hiking, others need a climbing gear), etc.