I started to use mailchimp and finds it very helpful.
However, I would like to add to my list a checkbox field, and cannot find it. I neither find a way to give a defaul
For MailChimp, the "checkbox" choices are a way to create a GROUP with different options for that group .. for which there is no default value.
Radio Buttons creates a field and does provide for a default value if nothing is entered.
The use of checkbox vs radiobutton is not just a UI choice, it is a functionality choice.
I hope this helps.