As you mention, one way to add "Category" information to your Info Items is using custom Attribute(s)[1]. You can later sort using this attribute (in the Related Items Pane[2]), search on the value (using an Advanced Search[3]), which would also provide a way to "group" the data as well.
You can also create custom templates[4], which could have a special default Icon and/or automatically have some or all of these custom attributes pre-assigned (even with default values if desired). The template of an Info Item is also searchable which provides an additional way to organize and identify Info Items. You can also later change the template of an Info Item (to another compatible template: any template based on the same Core[5] template is considered compatible).
Finally, you can assign the template of your choice as the Default Child Template attribute value to any Info Item, which determines the Info Item type that is created when inserting new child Info Items with the Insert key (or when dragging stuff from the clipboard onto an Info Item)...
[1]
http://www.kinook.com/UR/Manual/?attribute.htm
[2]
http://www.kinook.com/UR/Manual/?relateditemspane.htm
[3]
http://www.kinook.com/UR/Manual/?advancedsearch.htm
[4]
http://www.kinook.com/UR/Manual/?template.htm
[5]
http://www.kinook.com/UR/Manual/?coretemplates.htm