There is no limit on the number of tax-free savings accounts you can have.
The effect of compound interest, or earning investment return on investment return, is increased in a tax-free savings account due to the tax relief on the investment return. The longer you invest the more benefit you will get.
SARS will impose a tax penalty of 40% on excess contributions.
Yes, you can apply for a Tax-free Investment on behalf of your child or other family member, but keep in mind that you will be using part of their tax-free allowance, which may limit their ability to save for themselves via this type of product later.
A tax-free savings account can only be opened for an individual.