The configuration is done via an xml file called WEB-INF/validation.xml. There is a section near the top of the file containing all of the parameters that can be customized, with names that describe the actual entry field. e.g.

<constant>
  <constant-name>ENTRY_FIRST_NAME_MIN_LENGTH</constant-name>
  <constant-value>2</constant-value>
</constant>

Note that in order for modifications to take effect, the KonaKart application must be rebooted.

As for other data entered through the UI, validation for custom fields is set in WEB-INF/validation.xml . The file contains an example for a custom field where the minimum length is set to 5.

<field property="customerCustom1" depends="minlength">
    <arg0 key="register.customer.body.custom1"/>
    <arg1 name="minlength" key="${var:minlength}" 
          resource="false"/>
        <var>
            <var-name>minlength</var-name>
            <var-value>5</var-value>
        </var>
</field>