when asking so many questions at once, it is easy for some to fall through the cracks. It is a good practice to number your questions to help us ensure we don't miss any.
1) After selecting the one column option, did you click the apply button for the preview to be regenerated?
as for the question on minimum and maximum. This is enforcing the value of the checked checkboxes.
lets say you have for checkboxes:
check one: value=1
check two: value=2
check three: value=3
check four: value=4
setting the minimum to 2 and the maximum to four will cause validation to fail of 1 is selected, but pass if two or four is selected.
2) some foreign credit cards use cvv values that can contain letters.
3) the radio button option is not present because there is no good scenario for adding one radio button. If you only need one, you should be using a checkbox. A radio button should not be used outside of a group.
4) I think what you are missing when adding a new group, is that the have preset element definitions. what you are trying to accomplish is to customize the contact:comments group types.
For this you will need to select the group, click edit, add a new line after the email line. Select the added field, set it to select list, then click the edit button to populate the list with values.