1. There is currently no property of the combobox which allows you to limit the number of characters.
2. For the difference between ComboBox & MultiComboInput. ComboBox allows you to display large data sets, has UI virtualization, multiple different selection modes, multiple different dropdown options like resize, multiple auto-complete options, etc. The MultiComboInput’s purpose is to display small collection of items in a dropdown and to display them as tags.

Best regards,
Peter Stoev

Smart UI Team